Physics IGCSE Stephanie

Orbital Distance, Speed and Duration (Neptune)

Orbital distance/million km- 4495.1 Orbital Speed/km/s- 5.4 Orbital duration/days or years- 165 years

Hydroelectric Dams advantages

Can respond to demand so is reliable and available Can generate large scale amounts of electricity

Alpha, Beta & Gamma Emission

α, β and γ radiation can be identified by the emission from a nucleus by recalling their: Nature (what type of particle or radiation they are) Their relative ionising effects (how easily they ionise other atoms) Their relative penetrating abilities (how far can they travel before they are stopped completely) The properties of Alpha, Beta and Gamma are given in this table, and then described in more detail below

Approximate Density (kg/m3) of Water

1000

Energy store (Chemical)

Description- energy found in fuels, foods, or in batteries. This energy is transferred during chemical reactions

Energy store (Elastic)

Description- energy stored in a stretched spring or elastic band

Energy Transfer (Radiation)

Description- light and sound carry energy and can transfer this between two points

Energy Transfer (Heating)

Description- thermal energy can be transferred by conduction, convection or radiation

Comparing Transverse & Longitudinal Waves (Property- Density)

Transverse waves- constant density Longitudinal waves- changes in density

Applications of EM Waves Table (Gamma Rays)

sterilising medical instruments treating cancer

Comparing Transverse & Longitudinal Waves (Property- Pressure)

Transverse waves- pressure is constant Longitudinal waves- changes in pressure

Approximate Density (kg/m3) of Air

1.3

What can be used to measure length?

Ruler- used to measure small distance Tape Measure- used to measure larger distance Trundle Wheel- used to measure even larger distances

Applications of EM Waves Table (Radio)

Use- communication (radio and TV)

Experiment 1: Measuring the Density of Regularly Shaped Objects

1.Place the object on a digital balance and note down its mass 2.Use either the ruler, Vernier calipers or micrometer to measure the object's dimensions (width, height, length, radius) - the apparatus will depend on the size of the object 3.Repeat these measurements and take an average of these readings before calculating the density Calculate the volume of the object depending on whether it is a cube, sphere, cylinder (or other regular shape) Calculating the volume of an object depends on its shape Remember to convert from centimetres (cm) to metres (m) by dividing by 100 1 cm = 0.01 m 50 cm = 0.5 m Using the mass and volume, the density of each can be calculated using the equation: Where:ρ = density in kilogram per metres cubed (kg/m3)m = mass in kilograms (kg)V = volume in metres cubed (m3)

Force on a Current-Carrying Conductor

A current-carrying conductor produces its own magnetic field When interacting with an external magnetic field, it therefore will experience a force A current-carrying conductor will only experience a force if the current through it is perpendicular to the direction of the magnetic field lines A simple situation would be a copper rod placed within a uniform magnetic field When current is passed through the copper rod, it experiences a force which makes it move A copper rod moves within a magnetic field when current is passed through it Two ways to reverse the direction of the force (and therefore, the copper rod) are by reversing: The direction of the current The direction of the magnetic field

Comparing Conduction in Wood and Paper

A cylindrical rod made of half wood and half metal is wrapped tightly in paper Using a gentle flame, and holding the rod clear of the top of the flame, gently heat the paper at the join of the wood and metal Turn the rod so that the paper is well-heated all around the circumference of the rod Stop when the paper is clearly discoloured Remove the rod from the flame, gently unwrap the paper and observe the burn pattern A distinct pattern is seen; Where the paper touched the metal surface it is undamaged Where the paper touched the wood surface it is charred Explanation Metal is a good conductor of heat Where the paper touched the metal, heat was transferred from the paper into the metal and along the length of the metal This prevented the paper getting hot Wood is a good insulator, meaning it is a poor conductor of heat Where the paper touched the wood, heat was not transferred from the paper This meant that the paper did get hot enough to start to burn

Pressure in Liquids

A fluid is either a liquid or a gas When an object is immersed in a fluid, the fluid will exert pressure, squeezing the object This pressure is exerted evenly across the whole surface of the fluid and in all directions The pressure exerted on objects in fluids creates forces against surfaces These forces act at 90 degrees (at right angles) to the surface The pressure of a fluid on an object will increase with: Depth within the fluid Increased density of the fluid

What is a force?

A push or a pull that acts on an object due to the interaction with another object

Real Images

A real image is defined as: An image that is formed when the light rays from an object converge and meet each other and can be projected onto a screen A real image is one produced by the convergence of light towards a focus Real images are always inverted Real images can be projected onto pieces of paper or screens An example of a real image is the image formed on a cinema screen A real image can be projected onto a screen Real images are where two solid lines cross in ray diagrams

Resultant Forces on a Straight Line

A resultant force is a single force that describes all of the forces operating on a body When many forces are applied to an object they can be combined (added) to produce one final force which describes the combined action of all of the forces This single resultant force determines: The direction in which the object will move as a result of all of the forces The magnitude of the final force experienced by the object The resultant force is sometimes called the net force Forces can combine to produce: Balanced forces Unbalanced forces

Demonstrating Convection Currents

A simple demonstration of convection in liquids involves taking a beaker of water and placing a few crystals of potassium permanganate in it, to one side, as shown in the diagram above When the water is heated at that side, the potassium permanganate will dissolve in the heated water and rise along with the warmed water, revealing the convection current

Magnetic Effects of Changing Current

A solenoid can be used as an electromagnet by adding a soft iron core The iron core will become an induced magnet when current is flowing through the coils The magnetic field produced from the solenoid and the iron core will create a much stronger magnet overall The magnetic field produced by the electromagnet can be switched on and off When the current is flowing there will be a magnetic field produced around the electromagnet When the current is switched off there will be no magnetic field produced around the electromagnet An electromagnet consists of a solenoid wrapped around a soft iron core Changing the direction of the current also changes the direction of the magnetic field produced by the iron core

Reflection, Refraction & Diffraction

All waves, whether transverse or longitudinal, can be reflected, refracted and diffracted

Smoke Detectors

Alpha particles are used in smoke detectors The alpha radiation will normally ionise the air within the detector, creating a current The alpha emitter is blocked when smoke enters the detector The alarm is triggered by a microchip when the sensor no longer detects alpha In the diagram on the right, alpha particles are stopped by the smoke, preventing the flow of current and triggering the alarm

Electric Fields

Alpha particles have a charge of +2 (charge of a helium nucleus) Beta particles have a charge of −1 (charge of an electron) Therefore, between an electric field created between a negatively charged and positively charged plate Alpha particles are deflected towards the negative plate Beta particles are deflected towards the positive plate Gamma radiation is not deflected and travels straight through between the plates Alpha and Beta particles can be deflected by electric fields Alpha particles are heavier than beta particles Therefore, beta particles are deflected more in the electric field and alpha is deflected less

Conservation of Energy

Although an object in an elliptical orbit, such as a comet, continually changes its speed its energy must still be conserved Throughout the orbit, the gravitational potential energy and kinetic energy of the comet changes As the comet approaches the Sun: It loses gravitational potential energy and gains kinetic energy This causes the comet to speed up This increase in speed causes a slingshot effect, and the body will be flung back out into space again, having passed around the Sun As the comment moves away from the Sun: It gains gravitational potential energy and loses kinetic energy This causes it to slow down Eventually, it falls back towards the Sun once more In this way, a stable orbit is formed

Isotopes

Although the number of protons in a particular element is always the same, the number of neutrons can be different Isotopes are atoms of the same element that have an equal number of protons but a different number of neutrons This means that each element can have more than one isotope Isotopes tend to be more unstable due to their imbalance of protons and neutrons This means they're more likely to decay In the diagram below are three isotopes of Hydrogen: Hydrogen has three isotopes, each with a different number of neutrons Isotopes occur naturally, but some are more rare than others For example, about 2 in every 10,000 Hydrogen atoms is DeuteriumTritium is even more rare (about 1 in every billion billion hydrogen atoms)

Meters

Ammeters and voltmeters are used to measure the current and potential difference Ammeters are always connected in series whilst voltmeters are always connected in parallel

Digital or Analogue?

Ammeters can be either Digital (with an electronic read out) Analogue (with a needle and scale)

Benefits of Digital Signaling

An analogue signal consists of varying frequency or amplitude Examples of analogue technology include telephone transmission and some broadcasting A digital signal is generated and processed in two states:1 or 0 (high or low states respectively) Analogue v digital signal The key advantages of transmission of data in digital form compared to analogue are: The signal can be regenerated so there is minimal noise Due to accurate signal regeneration, the range of digital signals is larger than the range of analogue signals (they can cover larger distances)Digital signals enable an increased rate of transmission of data compared to analogue Extra data can be added so that the signal can be checked for errors

Atoms & Ions

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons An atom will lose or gain electrons to become more stable A stable atom is normally electrically neutral This means it has the same number of protons (positive charge) and electrons (negative charge) Positive ions are therefore formed when atoms lose electrons There will be more protons than electrons Negative ions are therefore formed when atoms gain electrons There will be more electrons than protons The difference between positive and negative ions

Orbits & Conservation of Energy

An object in an elliptical orbit around the Sun travels at a different speed depending on its distance from the Sun Although these orbits are not circular, they are still stable For a stable orbit, the radius must change if the comet's orbital speed changes As the comet approaches the Sun: The radius of the orbit decreases The orbital speed increases due to the Sun's strong gravitational pull As the comet travels further away from the Sun: The radius of the orbit increases The orbital speed decreases due to a weaker gravitational pull from the Sun Comets travel in highly elliptical orbits, speeding up as they approach the Sun

Decreasing Acceleration (Graph)

An object may accelerate at a decreasing rate On a speed-time graph this would be an downward curve

Constant Acceleration (Graph)

An object may accelerate at a steady rate, this is called constant acceleration On a speed-time graph this will be a non-horizontal straight line

Increasing Acceleration (Graph)

An object may accelerate at an increasing rate On a speed-time graph this would be an upward curve

Speeding Up & Slowing Down

An object that speeds up is accelerating An object that slows down is decelerating The acceleration of an object can be positive or negative, depending on whether the object is speeding up or slowing down If an object is speeding up, its acceleration is positive If an object is slowing down, its acceleration is negative (sometimes called deceleration)

Momentum

An object with mass that is in motion has momentum which is defined by the equation: momentum = mass × velocity p = mv Where: p = momentum in kilogram metre per second (kg m/s) m = mass in kilograms (kg) v = velocity in metres per second (m/s) This means that an object at rest (i.e v = 0) has no momentum Momentum keeps an object moving in the same direction, making it difficult to change the direction of an object with a large momentum Since velocity is a vector this means that the momentum of an object also depends on its direction of travel This means that momentum can be either positive or negative If an object travelling to the right has positive momentum, an object travelling in the opposite direction (to the left) will have negative momentum Therefore, the momentum of an object will change if: The object accelerates (speeds up) or decelerates (slows down) Changes direction Its mass changes

Measuring Time

Apparatus: stopwatch Unit: seconds (s) An important factor when measuring time intervals is human reaction time. This can have a significant impact upon measurements when the measurements involved are very short (less than a second)

Orbiting Objects or Bodies in Our Solar System (artificial satellite)

Body or Object- artificial satellite What it Orbits- any object or body in solar system

Orbiting Objects or Bodies in Our Solar System (moon)

Body or Object- moon What it Orbits- planet

Orbiting Objects or Bodies in Our Solar System (planet)

Body or Object- planet What it Orbits- sun

Boiling vs Evaporation

Boiling is also a change in state from liquid to gas Boiling happens only at the boiling point of the liquid The change of state happens all through the liquid (seen as bubbles in boiling water, for example)

Power supplies

Cells, batteries, power supplies and generators all supply current to the circuit

Describing the Nucleus

Define the terms proton number (atomic number) Z and nucleon number (mass number) A and be able to calculate the number of neutrons in a nucleus

Energy Transfer (Electrical)

Description- electricity can transfer energy from a power source, such as a cell, delivering it to components within a circuit

Energy store (Thermal)

Description- energy a substance has due to its temperature

Energy store (Gravitational)

Description- energy an object has due to its position above the ground. An object gains gravitational energy when lifted and loses it when it falls

Energy store (Nuclear)

Description- energy contained within the nucleus of an atom

Energy store (Electrostatic)

Description- energy due to the force of attraction (or repulsion) between two charges

Energy store (Magnetic)

Description-energy due to the force of attraction (or repulsion) between two magnets

Energy Transfer (Mechanical)

Description-when a force acts on a body e.g. a collision

Sankey Diagrams

Diagrams are used to represent energy transfers These are sometimes called Sankey diagrams The arrow in a Sankey diagram represents the transfer of energy: The end of the arrow pointing to the right represents the energy that ends up in the desired store (the useful energy output) The end(s) that point(s) down represents the wasted energy Total energy in, wasted energy and useful energy out shown on a Sankey diagram The width of each arrow is proportional to the amount of energy going to each store As a result of the conversation of energy: Total energy in = Useful energy out + Wasted energy A Sankey diagram for a modern efficient light bulb will look very different from that for an old filament light bulb A more efficient light bulb has less wasted energy This is shown by the smaller arrow downwards representing the heat energy

Calculating Efficiency

Efficiency is represented as a percentage, and can be calculated using the equation: EFFICIENCY = USEFUL ENERGY OUTPUT x100% TOTAL POWER OUTPUT The energy can be of any form e.g. gravitational potential energy, kinetic energy The efficiency equation can also be written in terms of power: EFFICIENCY = USEFUL ENERGY OUTPUT x100% TOTAL POWER OUTPUT Where power is defined as the energy transferred per unit of time Power = Energy transferred = E/t Time

Uses of Electromagnetic Waves

Electromagnetic waves have a variety of uses and applications The main ones are summarised in the table below:

What is friction in Solids?

Friction is a force that works in opposition to the motion of an object This slows down the motion of the object When friction is present, energy is transferred in the form of heat This raises the temperature (thermal energy) of the object and its surroundings The work done against the frictional forces causes this rise in the temperature Friction in solids is caused by imperfections in the surfaces of the objects moving over one another Not only does this slow the object down but also causes an increase in thermal energy

Sterilising Food and Medical Equipment

Gamma radiation is widely used to sterilise medical equipment Gamma is most suited to this because: It is the most penetrating out of all the types of radiation It is penetrating enough to irradiate all sides of the instruments Instruments can be sterilised without removing the packaging Food can be irradiated in order to kill any microorganisms that are present on it This makes the food last longer, and reduces the risk of food-borne infections Food that has been irradiated carries this symbol, called the Radura. Different countries allow different foods to be irradiated

Communications with Satellites

Geostationary and polar orbiting (low orbit) satellites are both used for communicating information Geostationary and polar orbits around the Earth

Geostationary Satellites

Geostationary satellites orbit above the Earth's equator The orbit of the satellite is 24 hours Has an orbit of 36 000 km above the Earth's surface, much higher than polar satellites Used for radio and telecommunication broadcasting around the world due to its high orbit Some satellite phones and direct broadcast satellite television use geostationary satellites

Hydrogen Isotopes

H-1 is the stable nucleus of hydrogen H-2 (deuterium) adds on one more neutron H-3 (tritium) adds on another neutron, making 2 neutrons to 1 proton. This is much more unstable than H-1 or H-2 If an nucleus is too heavy, this means it has too many protons and neutrons The forces in the nucleus will be weaker in keeping the protons and neutrons together This can also cause the nucleus to decay An example of this is Uranium-238 which is used in nuclear fission This nucleus has 238 protons and neutrons The decay of Uranium-238 gradually reduces the mass number of the element which it decays into This is done through alpha (α) or beta (β) decay

Average Kinetic Energy

Heating a system changes a substance's internal energy by increasing the kinetic energy of its particles The temperature of the material, therefore, is related to the average kinetic energy of the molecules This increase in kinetic energy (and therefore internal energy) can: Cause the temperature of the system to increase Or, produce a change of state (solid to liquid or liquid to gas) As the container heats up, the gas molecules move faster Faster motion causes higher kinetic energy and therefore higher internal energy

Condensation & Solidification

Heating and cooling graphs are used to : How the temperature of a substance changes when energy is transferred to or away from it Where changes of state occur Heating and cooling graphs tend to be the same Heating is when energy is transferred to the system and the kinetic energy of the molecules increases (red arrows to the right) Cooling is when energy is transferred away from the system (or dissipated to the surroundings) and the kinetic energy of the molecules decreases (blue arrows to the left)

Monochromatic Light

Light is a transverse wave The different colours of light all have different wavelengths (and frequencies)Red has the longest wavelength Violet has the shortest wavelength Light of a single wavelength (a single colour), or single frequency, is known as monochromatic The colours of the visible spectrum: red has the longest wavelength; violet has the shortest

Power

Machines, such as car engines, transfer energy from one energy store to another every second The rate of this energy transfer, or the rate of work done, is called power Since power is defined as The rate of doing work It can be expressed in equation form as P = W/t or P = ΔE/t Note that these two equations may be written slightly differently, but are representing the same thing - a transfer of energy store over time

Magnetic and Non-magnetic Materials

Magnetic materials are attracted to a magnet; non-magnetic materials are not Very few metals in the Periodic Table are magnetic. These include: Iron Cobalt Nickel Steel is an alloy which contains iron, so it is also magnetic Magnetic materials (which are not magnets) will always be attracted to the magnet, regardless of which pole is held close to it Magnetic materials attracted to magnets To test whether a material is a magnet it should be brought close to a known magnet If it can be repelled by the known magnet then the material itself is a magnet If it can only be attracted and not repelled then it is a magnetic material

Electromagnetic Components

Magnetising coils, relays and transformers use electromagnetic effects Relays use a small current in one circuit to switch on a much larger current in another Transformers 'step up' and 'step down' current and potential difference

Man-Made Sources

Medical sources In medicine, radiation is utilised all the time Uses include X-rays, CT scans, radioactive tracers, and radiation therapy Nuclear waste While nuclear waste itself does not contribute much to background radiation, it can be dangerous for the people handling it Nuclear fallout from nuclear weapons Fallout is the residue radioactive material that is thrown into the air after a nuclear explosion, such as the bomb that exploded at Hiroshima While the amount of fallout in the environment is presently very low, it would increase significantly in areas where nuclear weapons are tested Nuclear accidents Accidents such as that in Chernobyl contributed a large dose of radiation into the environment While these accidents are now extremely rare, they can be catastrophic and render areas devastated for centuries

Motion of Particles in a Gas

Molecules in a gas are in constant random motion at high speeds Random motion means that the molecules are travelling in no specific path and undergo sudden changes in their motion if they collide: With the walls of its container With other molecules Pressure in a gas is caused by the collisions with the surface (walls) of the container

Nuclear Mass

Nuclear mass is stated as the relative mass of the nucleus The term 'relative' refers to the mass of the particle divided by the mass of the proton The mass number is the total number of protons and neutrons in the nucleus The nucleon number (mass number) determines the relative mass of a nucleus

Changing Speed on a Distance-Time Graph

Objects might be moving at a changing speed This is represented by a curve In this case, the slope of the line will be changing If the slope is increasing, the speed is increasing (accelerating)If the slope is decreasing, the speed is decreasing (decelerating) The image below shows two different objects moving with changing speeds

Orbital Distance, Speed and Duration (Saturn)

Orbital distance/million km- 1433.5 Orbital Speed/km/s- 9.7 Orbital duration/days or years- 29.5 years

Worked Example Convert the following values between the Kelvin (absolute) and Celsius scales of temperature. a) 0 K = _______ °C b) 0 °C = _______ K c) 20 °C = _______ K

Part (a) Step 1: Choose whether to add or subtract 273 to the value The question is in kelvin therefore subtract 273 to convert to Celsius Step 2: Do the calculation Step 3: Write the answer with units 0K = −273 °C Part (b) Step 1: Choose whether to add or subtract 273 to the value The question is in Celsius therefore add 273 to convert to kelvin Step 2: Do the calculation Step 3: Write the answer with units 0 °C = 273 K Part (c) Step 1: Choose whether to add or subtract 273 to the value The question is in Celsius therefore add 273 to convert to kelvin Step 2: Do the calculation Step 3: Write the answer with units 20 °C = 293 K

Correcting Short-Sightedness

People who are short-sighted have eyes that are 'too large' This means they cannot see things that are far away, and only see things that are close to them This is because the eye refracts the light and brings it to a focus before it reaches the retinaIn other words, the focus point is in front of the retina at the back of the eye This can be corrected by using a concave or a diverging lens

Polar Satellites

Polar, or low orbit, satellites orbit around the Earth's north and south poles These orbit much lower than geostationary satellites, at around 200 km above sea level Used for monitoring the weather, military applications, and taking images of the Earth's surface There is a much shorter time delay for signals compared to geostationary orbit signals The signals and images are much clearer due to the lower orbit However, there is limited use in any one orbit because more than one satellites are required for continuous operation Some satellite phones use low-orbit artificial satellites if a more detailed signal is required

Measuring Potential Difference

Potential difference is measured using a voltmeter, which can be either Digital (with an electronic read out) Analogue (with a needle and scale) Voltmeters are connected in parallel with the component being tested The potential difference is the difference in electrical potential between two points, therefore the voltmeter has to be connected to two points in the circuit Analogue or Digital? Analogue voltmeters are subject to parallax error Always read the meter from a position directly perpendicular to the scale Typical ranges are 0.1-1.0 V and 0-5.0 A for analogue voltmeters although they can vary Always double check exactly where the marker is before an experiment, if not at zero, you will need to subtract this from all your measurements They should be checked for zero errors before using Voltmeters can be either analogue (with a scale and needle) or digital (with electronic read-out) Digital voltmeters can measure very small potential differences, in mV or µV Digital displays show the measured values as digits and are more accurate than analogue displays They're easy to use because they give a specific value and are capable of displaying more precise values However digital displays may 'flicker' back and forth between values and a judgement must be made as to which to write down Digital voltmeters should be checked for zero error Make sure the reading is zero before starting an experiment, or subtract the "zero" value from the end results Voltmeters are connected in parallel to the component being tested

Fuses

Protect expensive components from current surges and act as a safety measure against fire

Measuring Density (A suitable liquid e.g. sugar or salt solution)

Purpose- liquid to use to determine the density

Investigating Specific Heat Capacity (Equipment list) 1kg block of metal or a beaker containing a know mass of water

Purpose- substance to calculate the specific heat capacity

Investigating Specific Heat Capacity (Equipment list) Ammeter

Purpose- to determine the current form the power supply to the heater Resolution = 0.01A

Decay Equations

Radioactive decay events can be shown using a decay equation A decay equation is similar to a chemical reaction equation The particles present before the decay are shown before the arrow The particles produced in the decay are shown after the arrow During decay equations the sum of the mass and atomic numbers before the reaction must be the same as the sum of the mass and atomic numbers after the reaction The following decay equation shows Polonium-212 undergoing alpha decay It forms Lead-208 and an alpha particle An alpha particle can also be written as a helium nucleus (Symbol He) The polonium nucleus emits an alpha particle, causing its mass and charge to decrease. This means it changes into a new element

Investigating Refraction (Equipment list)

Ray Box- to provide a narrow beam of light to reflect in the mirror Protractor- to measure the light beam angles(resolution 1°) Sheet of paper- to mark with lines for angle measurements Pencil- to mark perpendicular lines and angle lines on paper Ruler- to draw lines on paper(resolution 1mm) Perspex blocks- to refract the light beam

Measuring Distance Using Supernovae

Redshift and CMB radiation allow various measurements of the Universe to be accurately made Measuring distance is done using different methods A key method is the use of standard candles, including supernovae Supernovae are exploding stars Certain types have the same peak level of brightness (absolute magnitude), making them extremely useful in measuring the distance to remote stars and galaxies Type 1a supernovae are so bright that they can be seen clearly even though they may be deep inside their parent galaxy This allows the distance to the galaxy to be calculated

Relative charge & mass (proton)

Relative charge- +1 Relative mass- 1

Ohm's Law

Resistance is the opposition to current For a given potential difference, the higher the resistance, the lower the current Therefore resistors are used in circuits to control the current The unit of resistance is the ohm, represented by the Greek symbol omega Ω The definition of resistance can be given using the equation R = V I Where R = resistance (ohms, Ω) V = potential difference (volts, V) I = current (amperes, A) Ohm's Law can be stated in words: Current is directly proportional to potential difference as long as the temperature remains constant

Advantages of solar panels

Solar energy is a renewable resource In many places on Earth sunlight is a reliable energy resource (this means that the sun shines most of the time) Solar panels produce no greenhouse gases or pollution once they are operating Solar panels can cut the cost of energy bills for households

Disadvantages to using solar cells

Solar farms need to be large scale to produce large amounts of electricity This is expensive to set up People often don't like the appearance of large solar farms, this is known as visual pollution In many places on Earth sunlight is not a reliable energy resource (there are not enough sunshine-hours to justify the set-up costs)

Disadvantages of solar panels

Solar furnaces need to be large scale to produce high temperatures Energy is still needed to heat water to a higher temperature in domestic households In many places on Earth sunlight is not a reliable energy resource (the sun doesn't shine regularly enough to justify the set-up costs)

Typical speeds in liquids, solid and gases

Solid- 5000m/s Liquid- 1500m/s Gas- 350m/s

Speed of Sound in Materials

Sound travels at different speeds in different mediums: Sound travels fastest in solids Sound travels slowest in gases

Describing Sound

Sound waves are produced by vibrating sources When a sound wave comes into contact with a solid, those vibrations can be transferred to the solid For example, sound waves can cause a drinking glass to vibrate If the glass vibrates too much the movement causes the glass to shatter Sound waves are longitudinal: the molecules vibrate in the same direction as the energy transfer Sound waves require a medium to travel through This means that if there are no molecules, such as in a vacuum, then the sound can't travel through it

Echoes

Sound waves reflect off hard surfaces The reflection of a sound wave is called an echo Echo sounding can be used to measure depth or to detect objects underwater A sound wave can be transmitted from the surface of the water The sound wave is reflected off the bottom of the ocean The time it takes for the sound wave to return is used to calculate the depth of the water The distance the wave travels is twice the depth of the ocean This is the distance to the ocean floor plus the distance for the wave to return Echo sounding is used to determine water depth

Speed of Sound in Air

Sound waves travel at a speed of about 340 m/s in air at room temperature The higher the air temperature, the greater the speed of sound The speed of sound in air varies from 330 - 350 m/s

Equation for solving the volume of an object

Sphere: 4/3 pie r3 Cube: d3 Cylinder: pie r2 × L

Gas

State- Gas Density- Low Arrangement of particles- Randomly arranged Movement of particles- Move quickly in all directions Energy of particles- Highest energy

The Earth's Axis

The Earth is a rocky planet that rotates in a near circular orbit around the Sun It rotates on its axis, which is a line through the north and south polesThe axis is tilted at an angle of approximately 23.4° from the vertical The Earth completes one full rotation (revolution) in approximately 24 hours (1 day) This rotation creates the apparent daily motion of the Sun rising and setting Rotation of the Earth on its axis is therefore responsible for the periodic cycle of day and night

The Solar System

The Solar System consists of: 1)The Sun 2)Eight planets 3)Natural and artificial satellites 4)Dwarf planets 5)Asteroids and comets

Nuclear Fusion

The Sun's energy is produced by through the process of nuclear fusion in its core Nuclear fusion involves the collision (and bonding) of hydrogen nuclei to form helium nuclei, releasing nuclear energy in the process Fusion is the process in which small nuclei, such as hydrogen, are fused together to form larger nuclei releasing energy in the process It is theoretically possible to produce a fusion reactor that could be used to generate electricity This technology could potentially solve the world's energy crisis Fusion requires extremely high temperatures, like in the centre of a star Scientists are currently researching how to sustain a fusion reaction at lower temperatures International research projects funded by some of the worlds largest businesses are making progress with some promising results Currently, the fusion reactions require nearly as much energy than they produce, but progress is being made toward net energy production If they succeed, virtually limitless amounts of energy could be produced, with large scale, carbon-free electricity generation

Calculating Specific Heat Capacity

The amount of energy needed to raise the temperature of a given mass by a given amount can be calculated using the equation: ΔQ = mcΔT Where: ΔQ = change in thermal energy, in joules (J) m = mass, in kilograms (kg) c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C) ΔT = change in temperature, in degrees Celsius (°C)

Differences in Exposure

The amount of radiation that a person receives is affected by a person's occupation, lifestyle or location Some areas around the world have higher background radiation because they are closer to sources of radiation People that work with nuclear radiation receive more radiationThe UK limit for nuclear industry employees is 20 mSv in one year The diagram below compares the dose received by some different activities All living things emit a small amount of radiation: the amount of radiation within a banana is tiny, and not at all dangerous!

Effects of Different Surfaces

The amount of thermal radiation emitted by an object depends on a number of factors: The surface colour of the object (black = more radiation) The texture of the surface (shiny surfaces = more radiation) The surface area of the object (greater surface area = more area for radiation to be emitted from) Black objects are very good at absorbing thermal radiation, for example black clothes make you feel hotter in sunny weather Black objects are also very good at emitting thermal radiation, which is the reason that chargers for laptops, and radiators in cars are coloured black - it helps them to cool down Shiny objects reflect thermal radiation and so absorb very little They also emit very little, though, and so take longer to cool down

White Dwarf

The core which is left behind will collapse completely, due to the pull of gravity, and the star will become a white dwarf The white dwarf will be cooling down and as a result, the amount of energy it emits will decrease

Current

The current is the amount of charge passing a point in a circuit every second (It is helpful to think of current as the charge per second) Charge, current and time are related by the following equation: CHARGE = CURRENT x TIME Q = I x t Where the symbols: Q stands for charge (measured in coulombs, C) I stands for current (measured in amps, A)

Advantages of fossil fuels

The current systems of transport and electricity generation rely heavily on fossil fuels which are generally readily available on a daily basis In the past fossil fuels have been reliable for large scale energy production although this is changing as supplies deplete and prices rise

Evidence from CMB Radiation

The discovery of the CMB (Cosmic Microwave Background) radiation led to the Big Bang theory becoming the currently accepted model The CMB is a type of electromagnetic radiation which is a remnant from the early stages of the Universe It has a wavelength of around 1 mm making it a microwave, hence the name Cosmic Microwave Background radiation In 1964, Astronomers discovered radiation in the microwave region of the electromagnetic spectrum coming from all directions and at a generally uniform temperature of 2.73 K They were unable to do this any earlier since microwaves are absorbed by the atmosphere Around this time, space flight was developed which enabled astronomers to send telescopes into orbit above the atmosphere According to the Big Bang theory, the early Universe was an extremely hot and dense environment As a result of this, it must have emitted thermal radiation The radiation is in the microwave region This is because over the past 14 billion years or so, the radiation initially from the Big Bang has become redshifted as the Universe has expanded Initially, this would have been high energy radiation, towards the gamma end of the spectrum As the Universe expanded, the wavelength of the radiation increased Over time, it has increased so much that it is now in the microwave region of the spectrum The CMB is a result of high energy radiation being redshifted over billions of years The CMB radiation is very uniform and has the exact profile expected to be emitted from a hot body that has cooled down over a very long time This phenomenon is something that other theories (such as the Steady State Theory) cannot explain The CMB map with areas of higher and lower temperature. Places with higher temperature have a higher concentration of galaxies, Suns and planets This is the closest image to a map of the observable Universe The different colours represent different temperatures The red / orange / brown regions represent warmer temperature indicating a higher density of galaxies The blue regions represents cooler temperature indicating a lower density of galaxies The temperature of the CMB radiation is mostly uniform, however, there are minuscule temperature fluctuations (on the order of 0.00001 K) This implies that all objects in the Universe are more or less uniformly spread out Measuring Galactic Speed & Distance

The Law of Reflection

The law of reflection states that these angles are the same: Angle of incidence (i) = Angle of reflection (r) Reflection of a wave at a boundary, i = r

Uses of Fossil Fuels (Transport)

The majority of vehicles in the world are powered by petroleum products such as petrol, diesel and kerosene These resources all originate from crude oil, which is a fossil fuel A growing number of vehicles are now being powered by electricity The advantage of this is that while the vehicle is being driven, it produces zero carbon emissions The disadvantage is that when the vehicle is being charged, it is connected to the National Grid, which currently uses a combination of renewable and non-renewable energy sources

Intermolecular Forces and Motion of Particles (Gases)

The molecules in a gas have more energy and move randomly at high speeds The molecules have overcome the forces holding them close together Because of the large spaces between the molecules The gas can easily be compressed and is also able to expand Gases flow freely

Intermolecular Forces and Motion of Particles (Liquids)

The molecules in a liquid have enough energy to overcome the forces between them They are still held close together The volume of the liquid is the same as the volume of the solid Molecules can move around (by sliding past each other) This allows the liquid to change shape and flow

X-rays

The most obvious use of x-rays is in medicine X-rays are able to pass through most body tissues but are absorbed by the denser parts of the body, such as bones When exposed to x-rays, the bones absorb the x-rays, leaving a shadow which can be seen using a special x-ray detector or photographic film

Evaporation & Cooling

The process of evaporation can be used to cool things down: If an object is in contact with an evaporating liquid, as the liquid cools the solid will cool as well This process is used in refrigerators and air conditioning units

Wave & Tide Power

The rise and fall of waves or the tide can be used to turn a turbine and generate electricity Underwater turbines generate electricity Tidal Barrage

The Speed of Electromagnetic Waves

The speed of electromagnetic waves in a vacuum is 3.0 × 10 8 m/s This is approximately the same speed as electromagnetic waves in air

Velocity

The velocity of a moving object is similar to its speed, except it also describes the object's direction The speed of an object only contains a magnitude - it's a scalar quantity The velocity of an object contains both magnitude and direction, e.g. '15 m/s south' or '250 mph on a bearing of 030°' Velocity is therefore a vector quantity because it describes both magnitude and direction The equation for velocity is very similar to the equation for speed: Where: v = velocity in metres per second (m/s)s = displacement, measured in metres (m)t = time, measured in seconds (s) Velocity is a vector quantity, so it uses displacement, s, rather than distance which is scalar.

Using a Balance

The weight of two objects can be compared using a balance Because the gravitational field strength is constant everywhere on Earth, this also allows us to measure the mass of an object m = W/g

Safety Considerations

There is a lot of glassware in this experiment, ensure this is handled carefully Water should not be poured into the measuring cylinder when it is on the electric balance This could lead to electric shock Make sure to stand up during the whole experiment, to react quickly to any spills

Comparing Transverse & Longitudinal Waves (Property- Vibration)

Transverse waves- 90 degrees to direction of energy transfer Longitudinal waves- parallel to direction of energy transfer

Comparing Transverse & Longitudinal Waves (Property- Vacuum)

Transverse waves- only electromagnetic waves can travel in vacuum Longitudinal waves-cannot travel in a vacuum

Wavefront

Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave The image below illustrates how wavefronts are visualised: The arrow shows the direction the wave is moving and is sometimes called a ray The space between each wavefront represents the wavelength When the wavefronts are close together, this represents a wave with a short wavelength When the wavefronts are far apart, this represents a wave with a long wavelength

Investigating Springs

When forces are applied to materials, the size and shape of the material can change The method below describes a typical procedure for carrying out an investigation into the properties of a material

Dangers of X-Rays & Gamma rays

X-rays and gamma rays are the most ionising types of EM waves They are able to penetrate the body and cause internal damage They can cause the mutation of genes and cause cancer Fortunately, the level of X-rays used in medicine is kept to minimum levels at which the risk is very low Doctors, however, will leave the room when taking X-rays in order to avoid unnecessary exposure to them People working with gamma rays have to take several precautions to minimise their exposure and are routinely tested to check their radiation dose levels For example, radiation badges are worn by medical professionals such as radiographers to measure the amount of radiation exposure in their body Radiation badges are used by people working closely with radiation to monitor exposure

Power rating (A railway engine)

1 000 000W = 1megawatt(MW) = 1 million watts

Wave Motion

Wave vibrations can be shown on ropes (transverse) and springs (longitudinal) Waves can be shown through vibrations in ropes or springs

Apparatus to investigate refraction

1)Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil 2)Switch on the ray box and direct a beam of light at the side face of the block 3)Mark on the paper: A point on the ray close to the ray box The point where the ray enters the block The point where the ray exits the block A point on the exit light ray which is a distance of about 5 cm away from the block 4)Draw a dashed line normal (at right angles) to the outline of the block where the points are 5)Remove the block and join the points marked with three straight lines 6)Replace the block within its outline and repeat the above process for a ray striking the block at a different angle 7)Repeat the procedure for each shape of perspex block (prism and semi-circular)

Investigating Thermal Radiation Method

1)Set up the four identical flasks painted black, grey, white and silver 2)Fill the flasks with hot water, ensuring the measurements start from the same initial temperature 3)Note the starting temperature, then measure the temperatures at regular intervals e.g. every 30 seconds for 10 minutes

Method 3: Measuring the speed of sound using an oscilloscope

1)Two microphones are connected to an oscilloscope and placed about 5 m apart using a tape measure to measure the distance 2)The oscilloscope is set up so that it triggers when the first microphone detects a sound, and the time base is adjusted so that the sound arriving at both microphones can be seen on the screen 3)Two wooden blocks are used to make a large clap next to the first microphone 4)The oscilloscope is then used to determine the time at which the clap reaches each microphone and the time difference between them 5)This is repeated several times and an average time difference calculated 6)The speed can then be calculated using the equation: SPEED OF SOUND = DISTANCE BETWEEN MICROPHONES TIME BETWEEN BREAKS

Power rating (World demand for power)

10 000 000MW

Power rating (A very large power station)

10 000MW

Power rating (An electric cooker)

10 000W = 10kW (1kW = 1000watts)

Power rating (A torch)

1W

Approximate Density (kg/m3) of Granite stone

2700

Approximate Density (kg/m3) of Wood

300-800 (depends on species)

Asteroids & Comets

Asteroids and comets also orbit the sun An asteroid is a small rocky object which orbits the Sun The asteroid belt lies between Mars and Jupiter Comets are made of dust and ice and orbit the Sun in a different orbit to those of planets The ice melts when the comet approaches the Sun and forms the comet's tail The objects in our solar system

Regulating Exposure

Because of the harmful effects of radiation, it is important to regulate the exposure of humans to radiation The amount of radiation received by a person is called the dose and is measured in sieverts (Sv) One sievert is a very big dose of radiationIt would cause acute radiation poisoning People would normally receive about 3 mSv (0.003 Sv) in one year To protect against over-exposure, the dose received by different activities is measured A dosemeter measures the amount of radiation in particular areas and is often worn my radiographers, or anyone working with radiation A dosemeter, or radiation badge, can be worn by a person working with radiation in order to keep track of the amount of radiation they are receiving

The momentum of a system before and after a collision

Before the collision: The momentum is only of mass m which is moving If the right is taken as the positive direction, the total momentum of the system is m × u After the collision: Mass M also now has momentum The velocity of m is now -v (since it is now travelling to the left) and the velocity of M is V The total momentum is now the momentum of M + momentum of m This is (M × V) + (m × -v) or (M × V) - (m × v)

what are the variety of ways forces can effect bodies?

Changes in speed: forces can cause bodies to speed up or slow down Changes in direction: forces can cause bodies to change their direction of travel Changes in shape: forces can cause bodies to stretch, compress, or deform

Fossil fuels are?

Coal Natural gas (mostly methane) which is used in domestic boilers and cookers Crude oil which is refined into petrol, diesel, and other fuels Fossil fuels: coal, oil and natural gas Fossil fuels are formed from the remains of plants and animals Chemical energy stored in fossil fuels originally came from sunlight Energy from the sun was transferred to the chemical energy store of plants by photosynthesis (plants use energy from sunlight to make food) Animals ate the plants and the energy was transferred to their chemical store

Investigate refraction (Analysis of Results)

Compare the different refraction patterns for each block Summary of the refraction patterns seen in different shaped blocks Angles i and r are always measured from the normal For light rays entering perspex block, the light ray refracts towards the central line: i > r For light rays exiting the perspex block, the light ray refracts away from the central line: i < r When the angle of incidence is 90° to the perspex block, the light ray does not refract, it passes straight through the block: i = r

Convection

Convection is the main way that heat travels through liquids and gases Convection only occurs in fluids Convection cannot happen in solids

Dangers of EM Waves (Visible light)

Danger- bright light can cause eye damage

Beta Decay Equation

During beta decay, a neutron changes into a proton and an electron The electron is emitted and the proton remains in the nuclei

Energy Flow Diagrams

Energy stores and transfers can be represented using a flow diagram This shows both the stores and the transfers

Geothermal energy disadvantages

Few suitable locations on Earth so small scale production of electricity Can result in the release of greenhouse gases from underground Expensive to build

Force & Momentum

Force can also be defined as the rate of change of momentum on a body The change in momentum is defined as the final momentum minus the initial momentum

Solar Panels & Heat Transfer

In many hot countries it is common for houses to produce hot water using solar panels Diagram showing a section through a solar panel

Combining Vectors by Calculation

In this method, a diagram is still essential but it does not need to be exactly to scale The diagram can take the form of a sketch, as long as the resultant, component and sides are clearly labelled Resultant Force = Effect of force 1 + Effect of force 2 Use Pythagoras' Theorem to find the resultant vector

Dangers of Radioactivity

Ionising radiation can damage human cells and tissues at high doses: This could be in terms of: Cell death Tissue damage Mutations Cancer As a result, its use needs to be kept to a minimum However, the benefits of using radiation in medicine can out way the potential risks The risks posed by the radiation are smaller than the risks associated with leaving the condition untreated For example, if a person has a cancerous tumour that is likely to kill them, then it is less of a risk to use radiotherapy than to leave the tumour

Disadvantages of fossil fuels

It takes millions of years for fossil fuels to form This is why they are considered to be a non-renewable energy resource The increasing demand for a decreasing supply causes prices to increase Fossil fuels are predicted to completely run out within the next 200 years Burning fossil fuels pollutes the atmosphere with harmful gases such as: Carbon dioxide which contributes to the greenhouse effect Sulphur dioxide which produces acid rain Both carbon and sulphur can be captured upon burning preventing it from being released into the atmosphere but this is expensive to do

Safety Considerations

Keep water away from all electrical equipment Make sure not to touch the hot water directly Run any burns immediately under cold running water for at least 5 minutes Do not overfill the kettle Make sure all the equipment is in the middle of the desk, and not at the end to avoid knocking over the beakers Carry out the experiment only whilst standing, in order to react quickly to any spills

Earthing

Many electrical appliances have metal cases This poses a potential safety hazard: If a live wire (inside the appliance) came into contact with the case, the case would become electrified and anyone who touched it would risk being electrocuted The earth wire is an additional safety wire that can reduce this risk If this happens: The earth wire provides a low resistance path to the earth It causes a surge of current in the earth wire and hence also in the live wire The high current through the fuse causes it to melt and break This cuts off the supply of electricity to the appliance, making it safe

Systems of Communications

Many important systems of communications rely on long wave electromagnetic radiation, including: Mobile phones, wireless internet & satellite television (using microwaves) Bluetooth, terrestrial television signals & local radio stations (using radio waves) Optical fibres (using visible or infrared waves)

What is used to measure the volume of liquids?

Measuring Cylinders can also be used to find the volume of an irregular shape.

Microwaves

Microwaves can be used to transmit signals over large distances Microwaves are used to send signals to and from satellites Mobile phones, wireless internet, satellite (global) television and monitoring Earth systems (for example, weather forecasting) all utilise microwave communication As with radio waves, microwaves signals will be clearer if there are no obstacles in the way which may cause diffraction of the beam On the ground, mobile phone signals use a network of microwave transmitter masts to relay the signals on to the nearest mast to the receiving phone They cannot be spaced so far apart that, for example, hills or the curvature of the Earth diffract the beam When microwaves are transmitted from a dish, the wavelength must be small compared to the dish diameter to reduce diffraction Also, the dish must be made of metal because metal reflects microwaves well Mobile phones and wireless internet use microwaves because microwaves are not refracted, reflected or absorbed by the atmosphere or ionosphere This means satellites can relay signals around the Earth enabling 24-hour-a-day communication all around the world Also, they can penetrate most walls and only require a short aerial for transmission and reception

Wave & Tide Power advantages

No pollution Reliable and can produce a large amount of electricity at short notice Renewable energy resource Small systems are being developed to provide electricity for small islands

Nuclear fuel advantages

No pollution released into atmosphere Nuclear reactors are perfectly safe as long as they are functioning properly Stringent checks must be routinely carried out and rigorous safety procedures followed Nuclear power stations can generate electricity reliably on a large scale which is available as needed

Analysing Orbits

Over many years, data about all the planets, moons and the Sun have been collected This is not just for general interest, but to indicate: Factors that affect conditions on the surface of the planets Environmental problems that a visit (using manned spaceships or robots) would encounter

Expected Results

Overall, metals are very good conductors whilst non-metals tend to be good insulators

Black Dwarf

Once the star has lost a significant amount of energy it becomes a black dwarf It will continue to cool until it eventually disappears from sight

Worked Example Describe the energy transfers in the following scenarios: a) A falling object b) A battery powering a torch c) A mass on a spring

Part (a) For a falling object: Energy is transferred from the gravitational store to the kinetic store of the object via a mechanical transfer pathway Part (b) For a battery powering a torch: Energy is transferred from the chemical store of the battery to the thermal store of the surroundings via a radiation transfer pathway Part (c) For a mass on a spring: Energy is transferred from the elastic store to the kinetic store of the system via a mechanical transfer pathway

Measuring Density (Digital balance)

Purpose- to measure the mass of the objects Resolution- 0.01g

Permanent Magnets

Permanent magnets are made out of permanent magnetic materials, for example steel A permanent magnet will produce its own magnetic field It will not lose its magnetism

Resistors

Potential dividers, fixed and variable resistors, thermistors and light-dependent resistors (LDRs) are all used to control current

Investigating Specific Heat Capacity (Equipment list) Thermometer

Purpose- to measure the temperature rise of the substance Resolution = 1 °C

Prisms

Prisms are used in a variety of optical instruments, including: Periscopes Binoculars Telescopes Cameras A periscope is a device that can be used to see over tall objects It consists of two right-angled prisms Reflection of light through a periscope The light totally internally reflects in both prisms Single and double reflection through right-angled prisms

Relative charge & mass (electron)

Relative charge- -1 Relative mass- 1/2000

Relative charge & mass (neutron)

Relative charge- 0 Relative mass- 1

Geothermal Energy advantages

Renewable resource Reliable source of energy Geothermal power stations are usually small compared to nuclear or fossil fuel power stations

Field Lines Between Two Oppositely Charged Parallel Conducting Plates

Some simple field patterns that you ought to know: The electric field between two parallel plates

Worked Example Lima did some online research and found out that the Moon orbits the Earth at a constant speed of around 2000 mph. She says that this is not an example of Newton's first law of motion. Is Lima correct? Explain your answer.

Step 1: Recall Newton's first law of motion Newton's first law of motion states that objects will remain at rest, or move with a constant velocity, unless acted on by a resultant force Step 2: Determine if the object in the question is at rest, or if it is moving with a constant velocity The Moon, in this case, is not at rest It is moving at a constant speed But it is not moving in a constant direction - it continually orbits the Earth Hence, it is not moving with a constant velocity, because velocity is a vector quantity Step 3: State and explain whether Lima is correct Lima is correct The Moon moves with a constant speed, but always changes direction So it is not moving with a constant velocity, and is not an example of Newton's first law of motion

Worked Example Two states of matter are described below. Identify each of the states of matter. Substance 1 molecules are spaced very far apart molecules move very quickly at random molecules move in a straight line Substance 2 molecules are quite closely packed together molecules move about at random molecules do not have fixed positions

Substance 1 Step 1: Identify the distances between the molecules The molecules are spaced far apart This can only describe a gas Step 2: Identify the motion of the molecules The molecules move quickly, at random and in a straight line This confirms that substance 1 is a gas Substance 2 Step 1: Identify the distances between the molecules The molecules are closely packed This could describe either a solid or a liquid Step 2: Identify the motion of the molecules The molecules move at random and do not have fixed positionsThis confirms that substance 2 is a liquid

Graphs for A.C. Generators

The A.C. generator creates an alternating current, varying in size and direction as the coil rotates The size of the induced EMF depends on the number of field lines it cuts The induced EMF is greatest (maximum value) when the coil is horizontal, or parallel with the field lines, as in this position it cuts through the field at the fastest rate The EMF is smallest (0) when the coil is vertical, or perpendicular with the field lines as in this position it will not be cutting through field lines Alternating EMF showing the position of the magnet relative to the coil When the magnet is in position 1 the magnetic field lines of the magnet do not cut the coil This means that there is no EMF induced in the coil When the magnet is in position 2 the magnetic field lines of the magnet are at 90° to the coil This means that there will be maximum EMF induced in the coil When the magnet is in position 3 the magnetic field lines of the magnet do not cut the coil This means that there is no EMF induced in the coil When the magnet is in position 4 the magnetic field lines of the magnet are at 90° to the coil This means that there will be maximum EMF induced in the coil As the poles of the magnet are reversed compared to position 2 the induced EMF will also be in the opposite direction compared to position 2 This means that the graph will show a negative trace

Evidence for the Big Bang

The Big Bang theory is very well supported by evidence from a range of sources The main pieces of evidence areGalactic red-shiftCosmic Microwave Background Radiation (CMBR)

Calculating Acceleration

The acceleration of an object can be calculated from the gradient of a speed-time graph Acceleration = gradient = rise/run

Investigating Specific Heat Capacity (Aims of the Experiment)

The aim of the experiment is to determine the specific heat capacity of a substance, by linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored Variables: Independent variable = Time, t Dependent variable = Temperature, θ Control variables: Material of the block Current supplied, I Potential difference supplied, V

Measure the length of all ball bearings

The blocks mark the edges of the first and last ball bearings The blocks make it easier to measure the length of all four ball-bearings Total length = 12 cm − 4 cm = 8 cm Step 2: Divide the total length by the number of ball-bearings Diameter = total length ÷ number of ball-bearings Diameter = 8 ÷ 4 Diameter = 2 cm

Uses & Consequences of Thermal Expansion (Consequences)

The expansion of solid materials can cause them to buckle if they get too hot This could include: Metal railway tracks Road surfaces Bridges Things that are prone to buckling in this way have gaps built in, this creates space for the expansion to happen without causing damage

Arrangement & Motion of Particles (Liquid)

The molecules are still close together (no gaps) but are no longer arranged in a regular pattern The molecules are able to slide past each other

Gamma Rays

The symbol for gamma is γ Gamma rays are electromagnetic waves They have the highest energy of the different types of electromagnetic waves Gamma rays have no charge

Factors Affecting the D.C Motor

The speed at which the coil rotates can be increased by Increasing the current Use a stronger magnet The direction of rotation of coil in the d.c motor can be changed by: Reversing the direction of the current Reversing the direction of the magnetic field by reversing the poles of the magnet The force supplied by the motor can be increased by: Increasing the current in the coil Increasing the strength of the magnetic field Adding more turns to the coil

Phases of the Moon

The way the Moon's appearance changes across a month, as seen from Earth, is called its periodic cycle of phases

Measuring the Speed of Sound

There are several experiments that can be carried out to determine the speed of sound Three methods are described below The apparatus for each experiment is given in bold

Types of Magnets

There are two types of magnets Permanent magnets Induced magnets

Uses & Consequences of Thermal Expansion (Applications)

Thermometers rely on the expansion of liquids to measure temperature Temperature-activated switches work when a bimetallic strip, consisting of two metals that expand at different rates, bends by a predictable amount at a given temperature The bimetallic strip will bend upwards when heated, closing the circuit

How the speed of a planet is affected by its distance from the Sun

This can be seen from data collected for a planet's orbital distance against their orbital speed

Investigating Refraction (Aim of the Experiment)

To investigate the refraction of light using rectangular blocks, semi-circular blocks and triangular prisms Variables Independent variable = shape of the block Dependent variable = direction of refraction Control variables:Width of the light beamSame frequency / wavelength of the light

Optical Fibres

Total internal reflection is used to reflect light along optical fibres, meaning they can be used for Communications Endoscopes Decorative lamps Safety reflectors on bicycles, cars and roads Light travelling down an optical fibre is totally internally reflected each time it hits the edge of the fibre Optical fibres utilise total internal reflection for communications Optical fibres are also used in medicine in order to see within the human body Endoscopes utilise total internal reflection to see inside a patient's body

High-Voltage Transmission

Transformers have a number of roles: They are used to increase the potential difference of electricity before it is transmitted across the national grid They are used to lower the high voltage electricity used in power lines to the lower voltages used in houses They are used in adapters to lower mains voltage to the lower voltages used by many electronic devices

Analogue Ammeters

Typical ranges are 0.1-1.0 A and 1.0-5.0 A for analogue ammeters Always double check exactly where the marker is before an experiment, if not at zero, you will need to subtract this from all your measurements. They should be checked for zero errors before using They are also subject to parallax error Always read the meter from a position directly perpendicular to the scale

Nuclear fuel disadvantages

Uranium ore found in the ground is used for fission reactions and since there is a finite supply Nuclear power is a non-renewable resource Nuclear fuels produce radioactive waste Radioactive waste needs to be stored for thousands of years Safe ways of storing radioactive waste is expensive If an accident occurs at a nuclear reactor, radioactive waste can leak out and spread over large areas

The Wave Equation

Wave speed is defined as: The distance travelled by a wave each second Wave speed is given the symbol ν and is measured in metres per second (m/s) Wave speed is the speed at which energy is transferred through a medium Transverse and longitudinal waves both obey the wave equation: Where: v = wave speed in metres per second (m/s)f = frequency in Hertz (Hz)λ = wavelength in metres (m) The wave speed equation may need to be rearranged, which can be done using this formula triangle

Wave Speed

Wave speed is the speed at which energy is transferred through a medium Wave speed is defined as: The distance travelled by a wave each second Wave speed is given the symbol, ν, and is measured in metres per second (m/s), it can be calculated using: wave speed = frequency × wavelength

Potential Difference in Series Circuits

When several cells are connected together in series, their combined EMF is equal to the sum of their individual EMFs The total EMF of these cells is equal to the s

Hydroelectric Dams

When water is stored above ground level it has energy in its gravitational potential store This energy can be transferred to kinetic energy if the water is allowed to flow down the slope Flowing water turns the turbine to generate electricity

Diffraction

When waves pass through a narrow gap, the waves spread out This effect is called diffraction Diffraction: when a wave passes through a narrow gap, it spreads out

Melting & Boiling

While a substance is changing state, either Melting or freezing Boiling or condensing The substance does not change temperature, even though energy is being transferred to or away from the thermal energy store of the substance

Applications of EM Waves Table (X-Rays)

X-Ray images (medicine, airport security)

Component vectors

are sometimes drawn with a dotted line and a subscript indicating horizontal or vertical

Equipment (Heatproof mat)

to protect the surface and to prevent heat loss from the bottom of the flask

What equation is used to calculate the pressure at the surface of a fluid?

he pressure at the surface of a fluid can be calculated using the equation: Force (N) P = F/A Pressure (Pa) Area (m3) Pressure is measured in the units Pascals (Pa) The area should always be the cross-sectional area of the object This means the area where the force is at right angles to it This equation tells us that: If a force is spread over a large area it will result in a small pressure If it is spread over a small area it will result in a large pressure

Worked Example A 58 g tennis ball moving horizontally to the left at a speed of 30 m s-1 is struck by a tennis racket which returns the ball back to the right at 20 m s-1.(i) Calculate the impulse delivered to the ball by the racket(ii) State which direction the impulse is in

(i) Step 1: Write the known quantities Taking the initial direction of the ball as positive (the left) Initial velocity, u = 30 m s-1 Final velocity, v = -20 m s-1 Mass, m = 58 g = 58 × 10-3 kg Step 2: Write down the impulse equation Impulse I = Δp = m(v - u) Step 3: Substitute in the values I = (58 × 10-3) × (-20 - 30) = -2.9 N s (ii) Direction of the impulse Since the impulse is negative, it must be in the opposite direction to which the tennis ball was initial travelling (since the left is taken as positive) Therefore, the direction of the impulse is to the right

Method 1: Measuring Sound Between Two Points

1)Two people stand a distance of around 100 m apart 2)The distance between them is measured using a trundle wheel 3)One person has two wooden blocks, which they bang together above their head 4)a stopwatch which they start when they see the first person banging the blocks together and stops when they hear the sound 5)This is then repeated several times and an average value is taken for the time 6)The speed of sound can then be calculated using the equation: SPEED OF SOUND = DISTANCE TRAVED BY SOUND TIME TAKEN

Experiment 2: Measuring the Density of Irregularly Shaped Objects

1. Place the object on a digital balance and note down its mass 2.Fill the eureka can with water up to a point just below the spout 3.Place an empty measuring cylinder below its spout 4.Carefully lower the object into the eureka can 5.Measure the volume of the displaced water in the measuring cylinder 6.Repeat these measurements and take an average before calculating the density Alternatively, the object can be placed in a measuring cylinder containing a known volume of liquid, and the change in volume then measured When an irregular solid is placed in a measuring cylinder, the level of the liquid will rise by an amount equal to the volume of the solid Once the mass and volume of the shape is known, its density can be calculated Analysis of Results The volume of the water displaced is equal to the volume of the object Once the mass and volume of the shape are known, the density can be calculated using:

Electric Fields (Extended)

A charged object creates an electric field around itselfThis is similar to the way in which magnets create magnetic fields This can be shown by electric field linesFields lines always point away from positive charges and towards negative charges Electric fields are always directed away from positive charges and towards negative charges The direction of the force lines in an electric field is described as: The direction of the force on a positive charge at that point Field lines show the direction that a positive charge would experience if it was at that point Although the definition of the force direction refers to a positive charge, in demonstrations it is always electrons (negative charges) which are free to move according to that force The strength of an electric field depends on the distance from the object creating the field: The field is strongest close to the charged object - this is shown by the field lines being closer together The field becomes weaker further away from the charged object - this is shown by the field lines becoming further apart

Conductors

A conductor is a material that allows charge (usually electrons) to flow through it easily Examples of conductors are: Silver Copper Aluminium Steel Conductors tend to be metals Different materials have different properties of conductivity On the atomic scale, conductors are made up of positively charged metal ions with their outermost electrons delocalised This means the electrons are free to move Metals conduct electricity very well because: Current is the rate of flow of charged particles So, the more easily electrons are able to flow, the better the conductor The lattice structure of a conductor with positive metal ions and delocalised electrons

Reducing Neutron Number

A nucleus decays to increase its stability by reducing the number of excess neutrons This is done by alpha or beta decay If the nucleus has too much energy, this is given off in the form of radiation This is often gamma radiation

Nuclide Notation

A nuclide is a group of atoms containing the same number of protons and neutrons For example, 5 atoms of oxygen are all the same nuclide but are 5 separate atoms Atomic symbols are written in a specific notation called nuclide or ZXA notation Atomic symbols in AZX Notation describe the constituents of nuclei The top number A represents the nucleon number or the mass number Nucleon number (A) = total number of protons and neutrons in the nucleus The lower number Z represents the proton or atomic number Proton number (Z) = total number of protons in the nucleus Note: In Chemistry, the nucleon number is referred to as the mass number and the proton number as the atomic number. The periodic table is ordered by atomic number An example of an atomic symbol is: mass number 7 Li atomic mass 3 Atomic symbols, like the one above, describe the constituents of nuclei When given an atomic symbol, you can figure out the total number of protons, neutrons and electrons in the atom: Protons: The number of protons is equal to the proton number Electrons: Atoms are neutral, and so in a neutral atom the number of negative electrons must be equal to the number of positive protons Neutrons: The number of neutrons can be found by subtracting the proton number from the nucleon number The term nucleon is used to mean a particle in the nucleus - ie. either a proton or a neutron The term nuclide is used to refer to a nucleus with a specific combination of protons and neutrons

Potential Difference in Parallel Circuits

A parallel circuit consists of two or more components attached along separate branches of the circuit Diagram showing two bulbs connected in parallel The advantages of this kind of circuit are: The components can be individually controlled, using their own switches If one component stops working the others will continue to function In a parallel circuit, the current splits up - some of it going one way and the rest going the other This means that the current in each branch will be smaller than the current from the power supply

Current in Parallel Circuits

A parallel circuit consists of two or more components attached along separate branches of the circuit Diagram showing two bulbs connected in parallel The advantages of this kind of circuit are: The components can be individually controlled, using their own switches If one component stops working the others will continue to function In a parallel circuit, the current splits up - some of it going one way and the rest going the other This means that the current in each branch will be smaller than the current from the power supply At a junction in a parallel circuit (where two or more wires meet) the current is conserved This means the amount of current flowing into the junction is equal to the amount of current flowing out of it This is because charge is conserved Note that the current does not always split equally - often there will be more current in some branches than in others The current in each branch will only be identical if the resistance of the components along each branch are identical Current behaves in this way because it is the flow of electrons: Electrons are physical matter - they cannot be created or destroyed This means the total number of electrons (and hence current) going around a circuit must remain the same When the electrons reach a junction, however, some of them will go one way and the rest will go the other Current is split at a junction into individual branches

Deflection in Electric & Magnetic Fields

A particle is deflected in an electric field if it has charge A particle is deflected in a magnetic field if it has charge and is moving perpendicular to it Therefore, since gamma (γ) particles have no charge, they are not deflected by either electric or magnetic fields Only alpha (α) and beta (β) particles are

Will polystyrene float and what is its density?

A polystyrene block will float in water This is because polystyrene has a density of 0.05 g/cm3 which is much less than the density of water (1.0 g/cm3)

Internal Energy

A rise in the temperature of an object increases its internal energy This can be thought of as due to an increase in the average speed of the particles Increasing speed increases kinetic energy Internal energy is defined as: The total energy stored inside a system by the particles that make up the system due to their motion and positions Motion of the particles affects their kinetic energy Positions of the particles relative to each other affects their potential energy Together, these two make up the internal energy of the system Substances have internal energy due to the motion of the particles and their positions relative to each other

Demonstrating Equilibrium

A simple experiment to demonstrate that there is no net moment on an object in equilibrium involves taking an object, such as a beam, and replacing the supports with newton (force) meters: The beam in the above diagram is in equilibrium The various forces acting on the beam can be found either by taking readings from the newton meters or by measuring the masses (and hence calculating the weights) of the beam and the mass suspended from the beam The distance of each force from the end of the ruler can then be measured, allowing the moment of each force about the end of the ruler to be calculated It can then be shown that the sum of clockwise moments (due to forces F2 and F3) equal the sum of anticlockwise moments (due to forces F1 and F4)

Demonstrating Different Rates of Thermal Conduction in Metals

A simple experiment to demonstrate the relative conducting properties of different materials can be carried out using apparatus similar to that shown in the diagram below The above apparatus consists of 4 different metal strips of equal width and length arrange around an insulated circle Ball bearings can be stuck to each of the strips and equal distance from the centre, using a small amount of wax The strips should then be turned upside down and the centre heated gently using a candle, so that each of the strips is heated at the point where they meet When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop By timing how long this takes for each of the strips, their relative thermal conductivities can be determined

Step-up & Step-down Transformers

A transformer consists of a primary and secondary coil The primary coil is the first coil The second coil is the second coil A step-up transformer increases the potential difference of a power source A step-up transformer has more turns on the secondary coil than on the primary coil (Ns > Np) A step-down transformer decreases the potential difference of a power source A step-down transformer has fewer turns on the secondary coil than on the primary coil (Ns < Np)

Virtual Images

A virtual image is defined as: An image that is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen A virtual image is formed by the divergence of light away from a point Virtual images are always upright Virtual images cannot be projected onto a piece of paper or a screen An example of a virtual image is a person's reflection in a mirror A reflection in a mirror is an example of a virtual image Virtual images are where two dashed lines, or one dashed and one solid line crosses in ray diagrams

Worked Example The diagram shows a rollercoaster going down a track. The rollercoaster takes the path A → B → C → D. Which statement is true about the energy changes that occur for the rollercoaster down this track? A. EK - ΔEP - ΔEP - EK B. EK - ΔEP - EK - ΔEP C. ΔEP - EK - EK - ΔEP D. ΔEP - EK - ΔEP - EK

ANSWER: D At point A: The rollercoaster is raised above the ground, therefore its gravitational potential energy store is full As it travels down the track, energy is transferred to its kinetic energy store mechanically At point B: Energy is transferred from the kinetic energy store to the gravitational potential energy store mechanically As the kinetic energy store empties, the gravitational potential energy store fills At point C: Energy is transferred from the gravitational potential energy store to the kinetic energy store At point D: The flat terrain means the rollercoaster only has energy in its kinetic energy store The kinetic energy store is full In reality, some energy will also be transferred to the thermal energy store of the tracks mechanically due to friction, and also to the thermal energy store of the surroundings by radiation due to sound. The total amount of energy in the system will be constant Total energy in = total energy out

Analysis of Results

All warm objects emit thermal radiation in the form of infrared waves The intensity (and wavelength) of the emitted radiation depends on: The temperature of the body (hotter objects emit more thermal radiation) The surface area of the body (a larger surface area allows more radiation to be emitted) The colour of the surface Most of the heat lost from the beakers will be due to conduction and convection This will be the same for each beaker, as colour does not affect heat loss in this way Any difference in heat loss between the beakers must, therefore, be due to infrared (thermal) radiation To compare the rate of heat loss of each flask, plot a graph of temperature on the y-axis against time on the x-axis and draw curves of best fit

Penetrating Power

Alpha, beta and gamma have different properties They penetrate materials in different ways This means they are stopped by different materials Alpha, beta and gamma are different in how they penetrate materials. Alpha is the least penetrating, and gamma is the most penetrating Alpha is stopped by paper, whereas beta and gamma pass through it Beta is stopped by a few millimeters of aluminium Gamma can pass through aluminium Gamma rays are only partially stopped by thick lead

Alternating Current (ac)

Alternating current typically comes from mains electricity and generators It is needed for use in transformers in the National Grid (covered later in this topic) The direction of electron flow changes direction regularly A typical frequency for the reversal of ac current in mains electricity is 50 Hz

Amplitude

Amplitude is defined as: The distance from the undisturbed position to the peak or trough of a wave It is given the symbol A and is measured in metres (m) Amplitude is the maximum or minimum displacement from the undisturbed position

Demonstrating Induction

An EMF can be induced either when: A conductor, such as a wire, cuts through a magnetic field The direction of a magnetic field through a coil changes Electromagnetic induction is used in: Electrical generators which convert mechanical energy to electrical energy Transformers which are used in electrical power transmission This phenomenon can easily be demonstrated with a magnet and a coil

Induced EMF

An EMF will be induced in a conductor if there is relative movement between the conductor and the magnetic field It will also be induced if the conductor is stationary in a changing magnetic field For an electrical conductor moving in a fixed magnetic field The conductor (e.g wire) cuts through the fields lines This induces an EMF in the wire Moving an electrical conductor in a magnetic field to induce an EMF When the magnet enters the coil, the field lines cut through the turns, inducing an EMF For a fixed conductor in a changing magnetic files As the magnet moved through the conductor (e.g. a coil), the field lines cut through the turns on the conductor (each individual wire)This induces an EMF in the coil A magnet moved towards a wire creates a changing magnetic field and induces a current in the wire A sensitive voltmeter can be used to measure the size of the induced EMF If the conductor is part of a complete circuit then a current is induced in the conductor This can be detected by an ammeter

Operation of a Transformer

An alternating current is supplied to the primary coil The current is continually changing direction This means it will produce a changing magnetic field around the primary coil The iron core is easily magnetised, so the changing magnetic field passes through it As a result, there is now a changing magnetic field inside the secondary coil This changing field cuts through the secondary coil and induces a potential difference As the magnetic field is continually changing the potential difference induced will be alternating The alternating potential difference will have the same frequency as the alternating current supplied to the primary coil If the secondary coil is part of a complete circuit it will cause an alternating current to flow

Transformer Efficiency

An ideal transformer would be 100% efficient Although transformers can increase the voltage of a power source, due to the law of conservation of energy, they cannot increase the power output If a transformer is 100% efficient: Input power = Output power The equation to calculate electrical power is: P = V × I Where: P = power in Watts (W) V = potential difference in volts (V) I = current in amps (A) Therefore, if a transformer is 100% efficient then: Vp × Ip = Vs × Is Where: Vp = potential difference across primary coil in volts (V) Ip = current through primary coil in Amps (A) Vs = potential difference across secondary coil in volts (V) Is = current through secondary coil in Amps (A) The equation above could also be written as: Ps = Vp × Ip Where:Ps = output power (power produced in secondary coil) in Watts (W)

Insulators

An insulator is a material that has no free charges, hence does not allow the flow of charge through them very easily Examples of insulators are: Rubber Plastic Glass Wood Some non-metals, such as wood, allow some charge to pass through them Although they are not very good at conducting, they do conduct a little in the form of static electricity For example, two insulators can build up charge on their surfaces. If those surfaces touch, this would allow that charge to be conducted away

Mass v Weight

An object's mass always remains the same, however, its weight will differ depending on the strength of the gravitational field on different planets For example, the gravitational field strength on the Moon is 1.63 N/kg, meaning an object's weight will be about 6 times less than on Earth

Ray Diagrams

Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary The angle of the wave approaching the boundary is called the angle of incidence (i) The angle of the wave leaving the boundary is called the angle of reflection (r) The line at right angles (90°) to the boundary is known as the normal When drawing a ray diagram an arrow is used to show the direction the wave is travelling An incident ray has an arrow pointing towards the boundary A reflected ray has an arrow pointing away from the boundary The angles of incidence and reflection are usually labelled i and r respectively A ray diagram for light reflecting at a boundary, showing the normal, angle of incidence and angle of reflection

The Big Bang

Around 14 billion years ago, the Universe began from a very small region that was extremely hot and dense Then there was a giant explosion, which is known as the Big Bang This caused the universe to expand from a single point, cooling as it does so, to form the universe today Each point expands away from the others This is seen from galaxies moving away from each other, and the further away they are the faster they move Redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory As a result of the initial explosion, the Universe continues to expand All galaxies are moving away from each other, indicating that the universe is expanding An analogy of this is points drawn on a balloon where the balloon represents space and the points as galaxies When the balloon is deflated, all the points are close together and an equal distance apart As the balloon expands, all the points become further apart by the same amount This is because the space itself has expanded between the galaxies A balloon inflating is similar to the stretching of the space between galaxies

Thermal Equilibrium

As an object absorbs thermal radiation it will become hotter As it gets hotter it will also emit more thermal radiation The temperature of a body increases when the body absorbs radiation faster than it emits radiation Eventually, an object will reach a point of constant temperature where it is absorbing radiation at the same rate as it is emitting radiation At this point, the object will be in thermal equilibrium An object will remain at a constant temperature if it absorbs heat at the same rate as it loses heat If the rate at which an object receives energy is less than the rate at which it transfers energy away then the object will cool down If the rate at which an object transfers energy away is less than the rate at which it receives energy then the object will heat up The process will always move towards thermal equilibrium

Potential Difference

As charge flows around a circuit energy is transferred from the power source to the charge carriers, and then to the components This is what makes components such as bulbs light up The potential difference between two points in a circuit is related to the amount of energy transferred between those points in the circuit Potential difference is defined as The work done by a unit charge passing through a component Potential difference is measure in volts (V) The potential difference is the difference in the electrical potential across each component: 5 volts for the bulb (on the left) and 7 volts for the resistor (on the right)

Energy Transfer in Electrical Circuits

As electricity passes around a circuit, energy is transferred from the power source to the various components (which may then transfer energy to the surroundings)As charge passes through the power supply it is given energy As it passes through each component it loses some energy (transferring that energy to the component) The current transfers electrical energy from the power source and to the components Different domestic appliances transfer energy from batteries, such as a remote control Most household appliances transfer energy from the AC mains This can be to the kinetic energy of an electric motor. Motors are used in: Vacuum cleaners - to create the suction to suck in dust and dirt off carpets Washing machines - to rotate the drum to wash (or dry) clothes Refrigerators - to compress the refrigerant chemical into a liquid to reduce the temperature Or, in heating devices. Heating is used in: Toasters - to toast bread Kettles - to boil hot water Radiators - hot water is pumped from the boiler so the radiator can heat up a room Energy transfers for a washing machine and toaster

Resistance of a Wire

As electrons pass through a wire, they collide with the metal ions in the wire Electrons collide with ions, which resist their flow The ions get in the way of the electrons, resisting their flow If the wire is longer, each electron will collide with more ions and so there will be more resistance: The longer a wire, the greater its resistance If the wire is thicker (greater diameter) there is more space for the electrons and so more electrons can flow: The thicker a wire, the smaller its resistance

Critical Angle

As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90° When the angle of refraction is exactly 90° the light is refracted along the boundary At this point, the angle of incidence is known as the critical angle c As the angle of incidence increases it will eventually surplus the critical angle and lead to total internal reflection of the light When the angle of incidence is larger than the critical angle, the refracted ray is now reflected This is total internal reflection

Dangers of Electromagnetic Waves

As the frequency of electromagnetic (EM) waves increases, so does the energy Beyond the visible part of the spectrum, the energy becomes large enough to ionise atoms As a result of this, the danger associated with EM waves increases along with the frequency The shorter the wavelength, the more ionising the radiation Although the intensity of a wave also plays a very important role Ultraviolet, X-rays and gamma rays can all ionise atoms Because of ionisation, ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue The effects depend on the type of radiation and the size of the dose They can damage cells and cause mutations, making them cancerous In general, electromagnetic waves become more dangerous the shorter their wavelength For example, radio waves have no known harmful effects whilst gamma rays can cause cancer and are regarded as extremely dangerous

I-V Graphs for Ohmic Resistors, Filament Lamps & Diodes

As the potential difference (voltage) across a component is increased, the current in the component also increases The precise relationship between voltage and current can be different for different types of components and is shown by an IV graph: IV graphs for a resistor and a filament lamp The IV graph for a resistor is very simple: The current is proportional to the potential difference This is because the resistor has a constant resistance For a lamp the relationship is more complicated: The current increases at a proportionally slower rate than the potential difference This is because: The current causes the filament in the lamp to heat up As the filament gets hot, its resistance increases This opposes the current, causing it to increase at a slower rate

What are moments?

As well as causing objects to speed up, slow down, change direction and deform, forces can also cause objects to rotate An example of a rotation caused by a force is on one side of a pivot (a fixed point that the object can rotate around) This rotation can be clockwise or anticlockwise A moment is defined as: The turning effect of a force about a pivot The size of a moment is defined by the equation: M = F × d Where: M = moment in newton metres (Nm) F = force in newtons (N) d = perpendicular distance of the force to the pivot in metres (m) This is why, for example, the door handle is placed on the opposite side to the hinge This means for a given force, the perpendicular distance from the pivot (the hinge) is larger This creates a larger moment (turning effect) to make it easier to open the door Opening a door with a handle close to the pivot would be much harder, and would require a lot more force Some other examples involving moments include: Using a crowbar to prize open something Turning a tap on or off A wheelbarrow Scissors

Atomic Structure

Atoms are the building blocks of all matter They are incredibly small, with a radius of only 1 × 10-10 m This means that about one hundred million atoms could fit side by side across your thumbnail Atoms have a tiny, dense nucleus at their centre, with electrons orbiting around the nucleus The radius of the nucleus is over 10,000 times smaller than the whole atom, but it contains almost all of the mass of the atom They consist of small dense positively charged nuclei, surrounded by negatively charged electrons An atom: a small positive nucleus, surrounded by negative electrons (Note: the atom is around 100,000 times larger than the nucleus!)

Experiment 1: Plotting the magnetic field around a wire

Attach the thick wire through a hole in the middle of the cardboard and secure it to the clamp stand Secure the wire vertically so it sits perpendicularly to the cardboard Attach the ends of the wire to a series circuit containing the variable resistor and ammeter on either side of the cell Using plotting compasses: Place plotting compasses on the card and draw dots at each end of the needle once it settles Make sure to draw an arrow to show the direction of the field at different points Move the compass so that it points away from the new dot, and repeat the process above Keep repeating the previous process until there is a chain of dots on the card Then remove the compass, or compasses, and link the dots using a smooth curve - this will be the magnetic field line Repeat the whole process several times to create several other magnetic field lines Using iron filings: If using iron filings, simply pour the filings onto the cards and gently shake the card until the filings settle in the pattern of the magnetic field around the wire

Experiment 2: Plotting the magnetic field around a solenoid

Attach the thick wire through a hole on one side of the cardboard and loop it through a hole on the other side of the cardboard and secure it to the clamp stand Secure the wire so it forms a circular loop around the cardboard Attach the ends of the wire to a series circuit containing the variable resistor and ammeter on either side of the cell Using plotting compasses: Follow the procedure outlined in Experiment 1 Note: this can be carried out using a solenoid, but since a solenoid is essentially many circular loops, the pattern around a circular loop can be extended to give the pattern around a solenoid Using iron filings and a solenoid: Take a solenoid (a metal slinky works well for this) and thread it through pre-made holes in a piece of card Pour the filings onto the card and gently shake the card until the filings settle in the pattern of the magnetic field around the solenoid

Sources of Background Radiation

Background radiation can come from natural sources on Earth or space and man-made sources

Background Radiation

Background radiation is radiation that is always present in the environment around us As a consequence, whenever an experiment involving radiation is carried out, some of the radiation that is detected will be background radiation When carrying out experiments to measure half-life, the presence of background radiation must be taken into account When measuring radioactive emissions, some of the detected radiation will be background To do this you must: Start by measuring background radiation (with no sources present) - this is called your background count Then carry out your experiment Subtract the background count from each of your readings, in order to give a corrected count The corrected count is your best estimate of the radiation emitted from the source, and should be used to measure its half-life

Accounting for Background Radiation

Background radiation must be accounted for when taking readings in a laboratory This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present This is known as the corrected count rate

What are balanced forces?

Balanced forces mean that the forces have combined in such a way that they cancel each other out and no resultant force acts on the body For example, the weight of a book on a desk is balanced by the normal force of the desk As a result, no resultant force is experienced by the book, the book and the table are equal and balanced

Bio fuels advantages

Biofuel is a renewable resource Some vehicles can be powered by biofuel rather than using fossil fuels Biofuel is considered to be carbon neutral No sulphur dioxide is produced

Orbiting Objects or Bodies in Our Solar System (asteroid)

Body or Object- asteroid What it Orbits- sun

Changes of State (Boiling & Condensing)

Boiling occurs when a liquid turns into a gas This is also called evaporating Condensing occurs when a gas turns into a liquid

Dangers of Microwaves

Certain frequencies of microwaves are absorbed by water molecules Since humans contain a lot of water, there is a risk of internal heating from microwaves This might worry some people, but microwaves used in everyday circumstances are proven to be safe Microwaves used for communications (including mobile phones) emit very small amounts of energy which are not known to cause any harm Microwave ovens, on the other hand, emit very large amounts of energy, however, that energy is prevented from escaping the oven by the metal walls and metal grid in the glass door

To Test Electrical Conductors and insulators

Charge the plate of the GLE so that the gold leaf stands clear of the rod Carefully touch the plate of the GLE with the items being tested, for example: Metals, such as: wire, paperclip, scissor blades Non-metals, such as: paper, fingers, glass, graphite Plastics, such as: plastic ruler, the handles of the scissors, finger in a plastic sandwich bag Comparisons, such as: wet cloth, dry cloth; finger and finger in a plastic sandwich bag Record the observations each time Leaf falls: material is a good conductor Leaf remains in place: object is a poor conductor (good insulator) Leaf falls slowly: material is a poor conductor

Thermal Conduction in Solids

Conduction is the main method of thermal energy transfer in solids Conduction occurs when: Two solids of different temperatures come in contact with one another, thermal energy is transferred from the hotter object to the cooler object Metals are the best thermal conductors This is because they have a high number of free electrons Conduction: the atoms in a solid vibrate and bump into each other Conduction can occur through two mechanisms: Atomic vibrations Free electron collisions When a substance is heated, the atoms, or ions, start to move around (vibrate) more The atoms at the hotter end of the solid will vibrate more than the atoms at the cooler end As they do so they bump into each other, transferring energy from atom to atom These collisions transfer internal energy until thermal equilibrium is achieved throughout the substance This occurs in all solids, metals and non-metals alike

Correcting Sight

Converging and diverging lenses are commonly used in glasses to correct defects of sight Converging lenses can be used to correct long-sighted vision Diverging lenses can be used to correct short-sighted vision

Count Rate

Count rate is the number of decays per second recorded by a detector and recorded by the counter It is measured in counts/s or counts/min The count rate decreases the further the detector is from the source This is because the radiation becomes more spread out the further away it is from the source

Bio fuels disadvantages

Crops of biofuel producing plants must be grown which takes time Growing the crops takes a lot of land, and takes resources needed for food production Burning biofuels releases carbon dioxide into the atmosphere It is considered carbon neutral because plants take in carbon dioxide when they photosynthesise

Direct Current and Alternating Current

Current can be direct current (dc) or alternating current (ac) In terms of calculations they can be treated in the same way Two graphs showing the variation of current with time for alternating current and direct current

Measuring Current

Current is measured using an ammeter Ammeters should always be connected in series with the part of the circuit you wish to measure the current through Ammeters measure the amount of charge passing through them per unit time, so the ammeter has to be in series so that all the charge flows through it An ammeter can be used to measure the current around a circuit

Dangers of EM Waves (Ultraviolet)

Danger- eye damage sunburn skin cancer

Dangers of EM Waves (Gamma rays)

Danger- kills cells mutations cancer

Dangers of EM Waves (X-Rays)

Danger- kills cells mutations cancer

Dangers of EM Waves (Microwave)

Danger- possible heat damage to internal organs

Dangers of EM Waves (Infrared)

Danger- skin burns

Energy store (Kinetic)

Description- energy an object has because it's moving

Density & Convection

Descriptions of convection currents always need to refer to changes in temperature causing changes in density The temperature may fall or rise, both can create a convection current When a liquid (or gas) is heated (for example by a radiator near the floor): The molecules push each other apart, making the liquid/gas expand This makes the hot liquid/gas less dense than the surroundings The hot liquid/gas rises, and the cooler (surrounding) liquid/gas moves in to take its place Eventually the hot liquid/gas cools, contracts and sinks back down again The resulting motion is called a convection current When a liquid (or gas) is cooled (for example by an A.C. unit high up on a wall): The molecules move together, making the liquid/gas contract This makes the hot liquid/gas more dense than the surroundings The cold liquid/gas falls, so that warmer liquid or gas can move into the space created The warmer liquid or gas gets cooled and also contracts and falls down The resulting motion is called a convection current

Investigating Diffraction

Diffraction can be shown in a ripple tank by placing small barriers and obstacles in the tank As the water waves encounter two obstacles with a gap between them, the waves can be seen to spread out as follows: Diffraction of water waves through a gap As the water waves encounter the edge of an obstacle, the waves can be seen to spread out as follows: Diffraction of water waves after passing an edge The amount of diffraction depends on the size of the gap compared to the wavelength of the water wave The diagram below shows how the wavelengths differ with frequency in a ripple tank The higher the frequency of the motor, the shorter the wavelength The lower the frequency of the motor, the longer the wavelength Ripple tank patterns for low and high frequency vibration

Factors Affecting Diffraction

Diffraction, as shown above, only generally happens when the gap is smaller than the wavelength of the wave As the gap gets bigger, the effect gradually gets less pronounced until, in the case that the gap is very much larger than the wavelength, the waves no longer spread out at all The size of the gap (compared to the wavelength) affects how much the waves spread out Diffraction can also occur when waves pass an edge When a wave goes past the edge of a barrier, the waves can curve around the edge

Digital Ammeters

Digital ammeters can measure very small currents, in mA or µA Digital displays show the measured values as digits and are more accurate than analogue displays They're easy to use because they give a specific value and are capable of displaying more precise values However digital displays may 'flicker' back and forth between values and a judgement must be made as to which to write down Digital ammeters should be checked for zero error Make sure the reading is zero before starting an experiment, or subtract the "zero" value from the end results Digital meter

Direct Current (dc)

Direct current is produced when using dry cells and batteries (and sometimes generators, although these are usually ac) The electrons flow in one direction only, from the negative terminal to the positive terminal

Examples of Vector

Displacement Velocity Weight Force Acceleration Momentum Electric field strength Gravitational field strength

Diverging Lens - Virtual Image

Diverging lenses can also be used to form images, although the images are always virtual in this case If an object is placed further from the lens than the focal length f then a diverging lens ray diagram will be drawn in the following way: Diverging lenses only produce virtual images Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly upwards away from the axis Draw a dashed line continuing this ray downwards to the focal point, f The image is the line drawn from the axis to the point where the above two rays meet In this case, the image is: Virtual: the light rays appear to meet when produced backwards Diminished: the image is smaller than the object Upright: the image is formed on the same side of the principal axis

Alpha Decay

During alpha decay an alpha particle is emitted from an unstable nucleus A completely new element is formed in the process Alpha decay usually happens in large unstable nuclei, causing the overall mass and charge of the nucleus to decrease An alpha particle is a helium nucleus It is made of 2 protons and 2 neutrons When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes The mass number decreases by 4 The atomic number decreases by 2 The charge on the nucleus also decreases by 2 This is because protons have a charge of +1 each

Beta Decay

During beta decay, a neutron changes into a proton and an electron The electron is emitted and the proton remains in the nuclei A completely new element is formed because the atomic number changes Beta decay often happens in unstable nuclei that have too many neutrons. The mass number stays the same, but the atomic number increases by one A beta particle is a high-speed electron It has a mass number of 0 This is because the electron has a negligible mass, compared to neutrons and protons Therefore, the mass number of the decaying nuclei remains the same Electrons have an atomic number of -1 This means that the new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay The following equation shows carbon-14 undergoing beta decay It forms nitrogen-14 and a beta particle Beta particles are written as an electron in this equation

Gamma Decay

During gamma decay, a gamma ray is emitted from an unstable nucleus The process that makes the nucleus less energetic but does not change its structure Gamma decay does not affect the mass number or the atomic number of the radioactive nucleus, but it does reduce the energy of the nucleus The gamma ray that is emitted has a lot of energy, but no mass or charge

Change to a New Element

During α-decay or β-decay, the nucleus changes to a different element The initial nucleus is often called the parent nucleus The nucleus of the new element is often called the daughter nucleus Alpha decay creating change a parent nucleus to a daughter nucleus of a new element The daughter nucleus is a new element because it has a different proton and/or nucleon number to the original parent nucleus This can be seen on a graph of N (neutron number) against Z (proton number) Graph of N against Z for the decay of Pu-239 When Pu-239 decays by alpha to U-235, it loses 2 protons and 2 neutrons U (Uranium) is a completely different element to Pu (Plutonium)

Field Lines Around a Point Charge

Electric charges create electric fields in the regions surrounding them, similar to the way in which magnets create magnetic fields The electric field is the region in which another charge will experience a force Fields lines always go away from positive charges and towards negative charges - they have the same direction as the direction of the force on a positively charged particle at a point in that field Electric fields are always directed away from positive charges and towards negative charges

Properties of Electromagnetic Waves

Electromagnetic waves are defined as: Transverse waves that transfer energy from the source of the waves to an absorber All electromagnetic waves share the following properties: They are all transverse They can all travel through a vacuum They all travel at the same speed in a vacuum The 7 types of electromagnetic waves together form a continuous spectrum

Relay Circuits

Electromagnets are commonly used in relay circuits Relays are switches that open and close via the action of an electromagnet A relay circuit consists of: An electrical circuit containing an electromagnet A second circuit with a switch which is near to the electromagnet in the first circuit When a current passes through the coil in Circuit 1, it attracts the switch in Circuit 2, closing it enables a current to flow in Circuit 2 When a current flows through Circuit 1, a magnetic field is induced around the coil The magnetic field attracts the switch, causing it to pivot and close the contacts in Circuit 2 This allows a current to flow in Circuit 2 When no current flows through Circuit 1, the magnetic force stops The electromagnet stops attracting the switch The current in Circuit 2 stops flowing Scrapyard cranes utilise relay circuits to function: When the electromagnet is switched on it will attract magnetic materials When the electromagnet is switched off it will drop the magnetic materials Electric bells also utilise relay circuits to function: Animation: Electric bells utilise relay circuits. As the current alternates, the metal arm strikes the bell and drops repeatedly to produce the ringing effect When the button K is pressed: A current passes through the electromagnet E creating a magnetic field This attracted the iron armature A, causing the hammer to strike the bell B The movement of the armature breaks the circuit at T This stops the current, destroying the magnetic field and so the armature returns to its previous position This re-establishes the circuit, and the whole process starts again Loudspeakers & Headphones Loudspeakers and headphones convert electrical signals into soundThey work due to the motor effect A loudspeaker consists of a coil of wire which is wrapped around one pole of a permanent magnet Diagram showing a cross-section of a loudspeaker An alternating current passes through the coil of the loudspeaker This creates a changing magnetic field around the coil As the current is constantly changing direction, the direction of the magnetic field will be constantly changing The magnetic field produced around the coil interacts with the field from the permanent magnet The interacting magnetic fields will exert a force on the coil The direction of the force at any instant can be determined using Fleming's left-hand rule As the magnetic field is constantly changing direction, the force exerted on the coil will constantly change direction This makes the coil oscillate The oscillating coil causes the speaker cone to oscillate This makes the air oscillate, creating sound waves

Uses of Electromagnets

Electromagnets use electricity to create a magnet from a current-carrying wire They have the advantage that they can be magnetised and demagnetised, literally at the flick of a switch They can be switched on and off Soft iron is the metal normally used for this It can easily become a temporary magnet Electromagnets have many uses including MRI scanners in hospitals; an MRI scanner is a large, cylindrical machine using powerful electromagnets to produce diagnostic images of the organs of the body Speakers and earphones; the loudspeakers, microphones and earphones used in phones and laptops use electromagnets to sense or send soundwaves Recycling; because steel is a magnetic material it can be easily separated from other metals and materials using electromagnets. Once recovered the steel is re-used and recycled, reducing mining for iron ore and processing ore into steelMag-Lev Trains; the ability of Mag-Lev trains to hover above the rails is due to them being repelled by large electromagnets on the train and track. This reduces friction and allows speeds of nearly 400 miles per hour

Conventional Current

Electrons are negatively charged This means that the electrons flow from negative to positive Conventional current, however, is still defined as going from positive to negative By definition, conventional current always goes from positive to negative (even though electrons go the other way)

Demonstrating Electrostatic Charges

Electrostatic repulsion is caused by the force between charges When these charges are the same as each other, they repel (push apart) In simple experiments showing the production of electrostatic charges by friction, insulating solids such as plastics are given a charge This is done using friction to transfer electrons from the surface By removing electrons, which have negative charge, the insulator is left with a positive charge Method: Suspend one of the insulating materials using a cradle and a length of string so that the material can rotate freely Rub one end of the material using a cloth (in order to give it a charge) Now take a second piece of insulating material and charge that by rubbing with a cloth Hold the charged end of the second piece close to the charged end of the first piece: If the first piece rotates away (is repelled) from the second piece then the materials have the same charge If the first piece moved towards (is attracted to) the second piece then they have opposite charges

Energy

Energy is a property that must be transferred to an object in order to perform work on or heat up that object It is measured in units of Joules (J) Energy will often be described as part of an energy system In physics, a system is defined as: An object or group of objects Therefore, when describing the changes within a system, only the objects or group of objects and the surroundings need to be considered Energy can be stored in different ways, and there are changes in the way it is stored when a system changes The principle of conservation of energy states that: Energy cannot be created or destroyed, it can only be transferred from one store to another This means that for a closed system, the total amount of energy is constant

Nuclear Fuel

Energy stored in the nucleus of atoms can be released when the nucleus is broken in two This is known as nuclear fission Nuclear Fission: when a large nucleus is broken into two smaller nuclei energy is released Nuclear power stations use fission reactions to heat water, to turn turbines to generate electricity

Measuring Energy Usage (The Kilowatt Hour (kWh)

Energy usage in homes and businesses is calculated and compared using the kilowatt hour The kilowatt hour is defined as: A unit of energy equivalent to one kilowatt of power expended for one hour Appliances are given power ratings, which tell consumers: The amount of energy transferred (by electrical work) to the device every second This kettle uses between 2500 and 3000 W of electrical energy This energy is commonly measured in kilowatt-hour (kW h), which is then used to calculate the cost of energy used

Cooling by Evaporation

Evaporation is a change in state of a liquid to a gas It happens; At any temperature Only from the surface of a liquid The molecules in a liquid have a range of energies Some have lots of energy, others have very little Their average energy relates to the temperature of the liquid Evaporation occurs when more energetic molecules moving near the surface of the liquid have enough energy to escape The average energy of the liquid is reduced Therefore liquids are cooled down by evaporation Evaporation occurs when more energetic molecules near the surface of a liquid escape

Electrical Energy Equation

Everyday appliances transfer electrical energy from the mains to other forms of energy in the appliance For example, in a heater, this will transfer electrical energy into a thermal energy store The amount of energy an appliance transfers depends on: How long the appliance is switched on for The power of the appliance A 1 kW iron uses the same amount of energy in 1 hour as a 2 kW iron would use in 30 minutes A 100 W heater uses the same amount of energy in 30 hours as a 3000 W heater does in 1 hour Calculating Electrical Energy To calculate electrical energy use the equation Where: E = energy (joules, J) V = voltage (volts, V) I = current (amps, A) t = time (seconds, s)

Example of pressure tractors

Example 1: Tractors Tractors have large tyres This spreads the weight (force) of the tractor over a large area This reduces the pressure which prevents the heavy tractor from sinking into the mud

Wave & Tide Power disadvantages

Expensive to build Damages fragile habitats Very few suitable locations The technology is not advanced enough for large scale electricity production

Thermal Conduction in Liquids & Gases

For thermal conduction to occur the particles need to be close together so that when they vibrate the vibrations are passed along This does not happen easily in fluids In liquids particles are close, but slide past each other In gases particles are widely spread apart and will not 'nudge' each other Both types of fluid, liquids and gases, are poor conductors of heat

How to Use Formula Triangles

Formula triangles are really useful for knowing how to rearrange physics equations To use them: Cover up the quantity to be calculated, this is known as the 'subject' of the equation Look at the position of the other two quantities If they are on the same line, this means they are multiplied If one quantity is above the other, this means they are divided - make sure to keep the order of which is on the top and bottom of the fraction! In the example below, to calculate speed, cover-up 'speed' and only distance and time are left This means it is equal to distance (on the top) ÷ time (on the bottom)

Uses of Fossil Fuels (Electricity Generation)

Fossil fuels, such as coal and oil, are used to produce energy on-demand when energy is needed This is done by burning the materials when the energy is required When coil is burned, it produces thermal energy This is used to boil water creating steam Steam is forced around the system and this turns a turbine The turbine turns coils in a magnetic field in the generator This generates electricity The electricity is transferred through a step-up transformer and is carried out of the system by electrical lines The steam within the turbine will cool and condense and then be pumped back into the boiler to repeat the process Electricity plays a bigger role in people's lives than ever before With almost 8 billion people in the world, this means the demand for electricity is extremely high To keep up with this demand, a combination of all the energy resources available is needed On the downside, the majority (84%) of the world's energy is still produced by non-renewable, carbon-emitting sources This has an enormous negative impact on the environment Currently, scientists are working hard to develop more and more efficient ways to produce electricity using more carbon-neutral energy resources

Frequency

Frequency is defined as: The number of waves passing a point in a second Frequency is given the symbol f and is measured in Hertz (Hz)

Choosing Which Fuse to Use

Fuses come in a variety of sizes (typically 3A, 5A and 13A) - in order to select the right fuse for the job, you need to know how much current an appliance needs If you know the power of the appliance (along with mains voltage), the current can be calculated using the equation: CURRENT = POWER VOLTAGE The fuse should always have a current rating that is higher than the current needed by the appliance, without being too high - always choose the next size up Example: Suppose an appliance uses 3.1 ampsA 3 amp use would be too small - the fuse would blow as soon as the appliance was switched onA 13 amp fuse would be too large - it would allow an extra 10 amps to pass through the appliance before it finally blewA 5 amp fuse would be an appropriate choice, as it is the next size up

Evidence from Galactic Red-Shift

Galactic redshift provides evidence for the Big Bang Theory and the expansion of the universe The diagram below shows the light coming to us from a close object, such as the Sun, and the light coming to the Earth from a distant galaxy Comparing the light spectrum produced from the Sun and a distant galaxy Red-shift provides evidence that the Universe is expanding because: Red-shift is observed when the spectral lines from the distant galaxy move closer to the red end of the spectrum This is because light waves are stretched by the expansion of the universe so the wavelength increases (or frequency decreases)This indicates that the galaxies are moving away from us Light spectrums produced from distant galaxies are red-shifted more than nearby galaxies This shows that the greater the distance to the galaxy, the greater the redshift This means that the further away a galaxy is, the faster it is moving away from the Earth These observations imply that the universe is expanding and therefore support the Big Bang Theory Tracing the expansion of the universe back to the beginning of time leads to the idea the universe began with a "big bang"

The Milky Way

Galaxies are made up of billions of stars The Universe is made up of many different galaxies The Sun is one of billions of stars in a galaxy called the Milky Way Other stars in the Milky Way galaxy are much further away from Earth than the Sun is Some of these stars also have planets which orbit them Our solar system is just one out of potentially billions in our galactic neighbourhood, the Milky Way. There are estimated to be more than 100 billion galaxies in the entire universe Astronomical distances such as the distances between stars and galaxies, are so large that physicists use a special unit to measure them called the light-year One light-year is: The distance travelled by light through (the vacuum of) space in one year The speed of light is the universal speed limit, nothing can travel faster than the speed of light But over astronomical distances, light actually travels pretty slowly The diameter of the Milky Way is approximately 100 000 light-years This means that light would take 100 000 years to travel across it One light year = 9.5 × 1012 km = 9.5 × 1015 m

Pressure & Force of Particles in a Gas

Gas molecules hit the sides of the container and exert a force, which creates pressure. A feature of gases is that they fill their container The pressure is defined as the force per unit area As the gas particles move about randomly they collide with the walls of their containers These collisions produce a net force at right angles to the wall of the gas container (or any surface) Therefore, a gas at high pressure has more frequent collisions with the container walls and a greater force Hence the higher the pressure, the higher the force exerted per unit area Gas molecules bouncing off the walls of a container It is possible to experience this force by closing the mouth and forcing air into the cheeks The strain on the cheeks is due to the force of the gas particles pushing at right angles to the cheeks

Properties of Gases

Gases have no definite shape and no fixed volume Gases can flow to take the shape of their container and are highly compressible

Experiments Demonstrating Thermal Conductors

Good thermal conductors are solids which easily transfer heatFor example; a metal pan or a ceramic tea cup Bad thermal conductors (also called insulators) are solids which do not transfer heat well For example; a woolen blanket or layers of cardboard or paper

Gravitational Field Strength

Gravitational field strength is defined as: The force per unit mass acting on an object in a gravitational field On Earth, this is equal to 9.8 N/kg Gravitational field strength is also known as acceleration of free fall, or acceleration due to gravityIn this context the units are m/s2 The value of g (gravitational field strength) varies from planet to planet depending on their mass and radius

Specific Heat Capacity

How much the temperature of a system increases depends on: The mass of the substance heated The type of material The amount of thermal energy transferred in to the system The specific heat capacity, c, of a substance is defined as: The amount of energy required to raise the temperature of 1 kg of the substance by 1 °C Different substances have different specific heat capacities If a substance has a low specific heat capacity, it heats up and cools down quickly (ie. it takes less energy to change its temperature) If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature) Low vs high specific heat capacity

Ultrasound

Humans can hear sounds between about 20 Hz and 20 000 Hz in frequency (although this range decreases with age) Humans can hear sounds between 20 and 20 000 Hz Ultrasound is the name given to sound waves with a frequency greater than 20 000 Hz

Demonstrating Lenz's Law

If a magnet is pushed north end first into a coil of wire then the end of the coil closest to the magnet will become a north pole Explanation Due to the generator effect, a potential difference will be induced in the coil The induced potential difference always opposes the change that produces it The coil will apply a force to oppose the magnet being pushed into the coil Therefore, the end of the coil closest to the magnet will become a north pole This means it will repel the north pole of the magnet Magnet being pushed into a coil of wire If a magnet is now pulled away from the coil of wire then the end of the coil closest to the magnet will become a south pole Explanation:Due to the generator effect, a potential difference will be induced in the coilThe induced potential difference always opposes the change that produces it The coil will apply a force to oppose the magnet being pulled away from the coil Therefore, the end of the coil closest to the magnet will become a south pole This means it will attract the north pole of the magnet Magnet being pulled away from a coil of wire

Disposing of Radioactive Waste

If an isotope has a long half-life then a sample of it will decay slowly Although it may not emit a lot of radiation, it will remain radioactive for a very long time Sources with long half-life values present a risk of contamination for a much longer time Radioactive waste with a long half-life is buried underground to prevent it from being released into the environment Radioactive waste with long half lifes are buried deep underground

The Greenhouse Effect

If the Earth had no atmosphere, the temperature on the surface would drop to about −180 °C at night, the same as the Moon's surface at night This would happen because the surface would be emitting all the radiation from the Sun into space The temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted The Earth receives the majority of its heat in the form of thermal radiation from the Sun At the same time, the Earth emits its own thermal radiation, with a slightly longer wavelength than the thermal radiation it receives (the surface temperature of the Earth is significantly smaller than the surface temperature of the Sun) Some gases in the atmosphere, such as water vapour, methane, and carbon dioxide (greenhouse gases) absorb and reflect back longer-wavelength infrared radiation from the Earth and prevent it from escaping into space These gases absorb the radiation and then emit it back to the surface This process makes the Earth warmer than it would be if these gases were not in its atmosphere The Earth receives thermal radiation from the Sun but emits its own thermal radiation at the same time The temperature of the Earth, therefore, depends on several factors, such as the rate that light and infrared radiation from the Sun are: Reflected back into space Absorbed by the Earth's atmosphere or by the Earth's surface Emitted from the Earth's surface and from the Earth's atmosphere into space

Mutations

If the atoms that make up a DNA strand are ionised then the DNA strand can be damaged If the DNA is damaged then the cell may die, or the DNA may be mutated when it reforms If a mutated cell is able to replicate itself then a tumour may form This is an example of cancer, which is a significant danger of radiation exposure Diagram showing the damage caused to DNA by ionising radiation. Sometimes the cell is able to successfully repair the DNA, but incorrect repairs can cause a mutation Acute radiation exposure can have other serious symptoms: It can cause skin burns, similar to severe sunburn Radiation can reduce the amount of white blood cells in the body, making a person more susceptible to infections by lowering their immune system Because of this, it is very important to handle radioactive sources carefully

Magnifying Glasses

If the object is placed closer to the lens than the focal length, the emerging rays diverge and a real image is no longer formed When viewed from the right-hand side of the lens, the emerging rays appear to come from a point on the leftThis point can be found by extending the rays backwards (creating virtual rays) A virtual image will be seen at the point where these virtual rays cross A virtual image is formed by the divergence of rays from a point In this case the image is: Virtual Enlarged Upright Using a lens in this way allows it to be used as a magnifying glass When using a magnifying glass, the lens should always be held close to the object

Boyle's Law

If the temperature T of an ideal gas is constant, then Boyle's Law is given by: P x 1/V This means the pressure is inversely proportional to the volume of a gas The relationship between the pressure and volume for a fixed mass of gas at constant temperature can also be written as: P1 V1 = P2 V2 Where: P1 = initial pressure (Pa) P2 = final pressure (Pa) V1 = initial volume (m3) V2 = final volume (m3) Notice that volume and pressure are measured in m3 and Pa respectively In calculations if units are given in cm3 or MPa this is a rare case where calculations can be done using the original units as long as answers are reported in the same, original units

The Gas Laws (Pressure & Volume (Constant Temperature)

If the temperature of a gas remains constant, the pressure of the gas changes when it is: Compressed - decreases the volume which increases the pressure Expanded - increases the volume which decreases the pressure Pressure increases when a gas is compressed Similarly, a change in pressure can cause a change in volume A vacuum pump can be used to remove the air from a sealed container The diagram below shows the change in volume to a tied up balloon when the pressure of the air around it decreases: When a gas is compressed, the molecules will hit the walls of the container more frequentlyThis creates a larger overall net force on the walls which increases the pressure

Real & Virtual Images

Images produced by lenses can be one of two types: A real image A virtual image

Rutherford's Experiment

In 1909 a group of scientists were investigating the Plum Pudding model Physicist, Ernest Rutherford was instructing two of his students, Hans Geiger and Ernest Marsden to carry out the experiment This involved the scattering of alpha (α) particles by a sheet of thin metal supports the nuclear model of the atom A beam of alpha particles (He2+ ions) were directed at a thin gold foil They expected the alpha particles to travel through the gold foil, and maybe change direction a small amount Instead, they discovered that : Most of the alpha particles passed straight through the foil Some of the alpha particles changed direction but continued through the foil A few of the alpha particles bounced back off the gold foil The bouncing back could not be explained by the Plum Pudding model, so a new model had to be created This was the first evidence of the structure of the atom When α-particles are fired at thin gold foil, most of them go straight through but a very small number bounce straight back When α-particles are fired at thin pieces of gold foil: The majority of them go straight through (A) This happens because the atom is mainly empty space Some are deflected through small angles (B) This happens because the positive α-particles are repelled by the positive nucleus which contains most of its mass A very small number are deflected straight back (C) This is because the nucleus is extremely small

Hubble Constant Calculations

In 1929, the astronomer Edwin Hubble showed that the universe was expanding He did this by observing that the absorption line spectra produced from the light of distant galaxies was shifted towards the red end of the spectrum This doppler shift in the wavelength of the light is evidence that distant galaxies are moving away from the Earth Hubble also observed that light from more distant galaxies was shifted further towards the red end of the spectrum compared to closer galaxies From this observation he concluded that galaxies or stars which are further away from the Earth are moving faster than galaxies which are closer Hubble's law states: The recessional velocity v of a galaxy is proportional to its distance from Earth Hubble's law can be expressed as an equation: H0 = v d Where: H0 = Hubble constant, this will be provided in your examination along with the correct units (s-1) The accepted value is that H0 = 2.2 × 10-18 per second v = recessional velocity of an object, the velocity of an object moving away from an observer (km s-1) d = distance between the object and the Earth (km) As the equation shows, the Hubble Constant, H0 is defined as: The ratio of the speed at which the galaxy is moving away from the Earth, to its distance from the Earth

Current in Series Circuits

In a circuit that is a closed-loop, such as a series circuit, the current is the same value at any point This is because the number of electrons per second that passes through one part of the circuit is the same number that passes through any other part This means that all components in a closed-loop have the same current The current is the same at each point in a closed-loop The amount of current flowing around a series circuit depends on two things: The voltage of the power source The number (and type) of components in the circuit Increasing the voltage of the power source drives more current around the circuit So, decreasing the voltage of the power source reduces the current Increasing the number of components in the circuit increases the total resistance Hence less current flows through the circuit Current will increase if the voltage of the power supply increases, and decreases if the number of components increases (because there will be more resistance)

Converging Lenses

In a converging lens, parallel rays of light are brought to a focus This point is called the principal focus This lens is sometimes referred to as a convex lens The distance from the lens to the principal focus is called the focal length This depends on how curved the lens is The more curved the lens, the shorter the focal length The focal length is the distance from the lens to the principal focus

Diverging Lenses

In a diverging lens, parallel rays of light are made to diverge (spread out) from a point This lens is sometimes referred to as a concave lens The principal focus is now the point from which the rays appear to diverge from Parallel rays from a diverging lens appear to come from the principal focus

Diodes

In addition to the above, you should be able to recognise and draw the circuit symbol for a diode: A diode is a component that only allows a current in one direction (Note: diodes are occasionally drawn with a horizontal line running through the middle of them) If a diode is connected to an a.c. (alternating current) power supply, it will only allow a current half of the time (This is called rectification) A diode can be used to rectify an alternating current

Ultrasound in Industry

In industry, ultrasound can be used to: Check for cracks inside metal objects Generate images beneath surfaces A crack in a metal block will cause some waves to reflect earlier than the rest, so will show up as pulses on an oscilloscope trace Each pulse represents each time the wave crosses a boundary The speed of the waves is constant, so measuring the time between emission and detection can allow the distance from the source to be calculated Ultrasound is partially reflected at boundaries, so in a bolt with no internal cracks, there should only be two pulses (at the start and end of the bolt)

Electrical Power Equation

In mechanics, power P is defined as the rate of doing work The potential difference is the work done per unit charge Current is the rate of flow of charge Therefore, the electrical power is defined as the rate of change of work done: The work done is the energy transferred so the power is the energy transferred per second in an electrical component The power dissipated (produced) by an electrical device can also be written as Using Ohm's Law V = IR to rearrange for either V or I and substituting into the power equation, means power can be written in terms of resistance R This means for a given resistor if the current or voltage doubles the power will be four times as great. Which equation to use will depend on whether the value of current or voltage has been given in the question Rearranging the energy and power equation, the energy can be written as: E = VIt Where: E = energy transferred (J) V = potential difference (V) I = current (A) t = time (s)

Ultrasound in Medicine

In medicine, ultrasound can be used: To construct images of a foetus in the womb To generate 2D images of organs and other internal structures (as long as they are not surrounded by bone) As a medical treatment such as removing kidney stones An ultrasound detector is made up of a transducer that produces and detects a beam of ultrasound waves into the body The ultrasound waves are reflected back to the transducer by boundaries between tissues in the path of the beam For example, the boundary between fluid and soft tissue or tissue and bone When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner Using the speed of sound and the time of each echo's return, the detector calculates the distance from the transducer to the tissue boundary By taking a series of ultrasound measurements, sweeping across an area, the time measurements may be used to build up an image Unlike many other medical imaging techniques, ultrasound is non-invasive and is believed to be harmless Ultrasound can be used to construct an image of a foetus in the womb

Complex Consequences of Energy Transfer

In real situations there is very rarely only one form of energy transfer Usually all three happen at once In the diagram below a more complex - and more 'real' - version of the situation above is shown Thermal energy is transferred from hotter areas (the tea) to cooler areas (the cup, hands and air) by the processes of: Conduction; by direct contact between the tea and the solid sides of the cup and also by direct contact from the cup to the surface it is sitting on Convection; from the surface of the coffee to the air directly above it Radiation; from the sides of the hot cup in all directions to the surrounding air Objects will always lose heat until they are in thermal equilibrium (same temperature) with their surroundings For example, a mug of hot tea will cool down until it reaches room temperature Eventually the room, tea and cup will all be at the same temperature

Nuclear Fusion in Stars

In the centre of a stable star, hydrogen atoms undergo nuclear fusion to form helium The equation for the reaction is shown here: Deuterium and Tritium are both isotopes of hydrogen. They can be formed through other fusion reactions in the star A huge amount of energy is released in the reaction This provides a pressure that prevents the star from collapsing under its gravity The fusion of deuterium and tritium to form helium with the release of energy

Phases of the Moon as it orbits around Earth

In the image above, the inner circle shows that exactly half of the Moon is illuminated by the Sun at all times The outer circle shows how the Moon looks like from the Earth at its various positions In the New Moon phase: The Moon is between the Earth and the Sun Therefore, the sunlight is only on the opposite face of the Moon to the Earth This means the Moon is unlit as seen from Earth, so it is not visible At the Full Moon phase: The Earth is between the Moon and the Sun The side of the Moon that is facing the Earth is completely lit by the sunlight This means the Moon is fully lit as seen from Earth In between, a crescent can be seen where the Moon is partially illuminated from sunlight

Infrared

Infrared is emitted by warm objects and can be detected using special cameras (thermal imaging cameras). These can be used in industry, in research and also in medicine Many security cameras are capable of seeing slightly into the infrared part of the spectrum and this can be used to allow them to see in the dark Infrared lights are used to illuminate an area without being seen, which is then detected using the camera Remote controls also have small infrared LEDs that can send invisible signals to an infrared receiver on a device such as a TV Infrared travels down fibre optic cables more efficiently than visible light, and so most fibre optic communication systems use infrared

Ionising Effect of Radiation

Ionisation is the process of which an atom becomes negative or positive by gaining or losing electrons All nuclear radiation is capable of ionising atoms that it hits When an atom is ionised, the number of electrons it has changes This is mostly done by knocking out an electron so the atom loses a negative charge and is left overall positive When radiation passes close to atoms it can knock out electrons, ionising the atom Alpha is by far the most ionising form of radiation Alpha particles leave a dense trail of ions behind them, affecting virtually every atom they meet Because of this they quickly lose their energy and so have a short range Their short range makes them relatively harmless if handled carefully, but they have the potential to be extremely dangerous if the alpha emitter enters the body Beta particles are moderately ionising The particles create a less dense trail of ions than alpha, and consequently have a longer range They tend to be more dangerous than alpha because they are able to travel further and penetrate the skin, and yet are still ionising enough to cause significant damage Gamma is the least ionising form of radiation (although it is still dangerous) Because Gamma rays don't produce as many ions as alpha or beta, they are more penetrating and have a greater range This can make them hazardous in large amounts The ionising effects depend on the kinetic energy and charge of the type of radiation The greater the charge of the radiation, the more ionising it is This means alpha radiation is the most ionising as it has a charge of +2 A beta particle has a charge of -1 so is moderately ionising This means gamma radiation is the least ionising as it has a charge of 0 (no charge) The higher the kinetic energy of the radiation, the more ionising it is This means alpha particle is still the most ionising because it has the greatest mass However, a beta particle is very light (it is an electron) but travels at high speeds, therefore, it has a lot of kinetic energy and is still moderately ionising Gamma radiation has virtually no mass so is weakly ionising

Detecting Radiation

It is important to regulate the exposure of humans to radiation The amount of radiation received by a person is called the dose Ionising nuclear radiation is measured using a detector connected to a counter

Background Radiation

It is important to remember that radiation is a natural phenomenon Radioactive elements have always existed on Earth and in outer space However, human activity has added to the amount of radiation that humans are exposed to on Earth Background radiation is defined as: The radiation that exists around us all the time There are two types of background radiation: Natural sources Man-made sources Background radiation is the radiation that is present all around in the environment. Radon gas is given off from some types of rock Every second of the day there is some radiation emanating from natural sources such as: Rocks Cosmic rays from space Foods Although most background radiation is natural, a small amount of it comes from artificial sources, such as medical procedures (including X-rays) Levels of background radiation can vary significantly from place to place

Half-Life Basics

It is impossible to know when a particular unstable nucleus will decay But the rate at which the activity of a sample decreases can be known This is known as the half-life Half-life is defined as: The time taken for half the nuclei of that isotope in any sample to decay In other words, the time it takes for the activity of a sample to fall to half its original level Different isotopes have different half-lives and half-lives can vary from a fraction of a second to billions of years in length Half-life can be determined from an activity-time graph The graph shows how the activity of a radioactive sample changes over time. Each time the original activity halves, another half-life has passed The time it takes for the activity of the sample to decrease from 100 % to 50 % is the half-life It is the same length of time as it would take to decrease from 50 % activity to 25 % activity The half-life is constant for a particular isotope Half-life can also be represented on a table As the number of half life increases, the proportion of the isotope remaining halves

Features of Lens Diagrams

Lens diagrams can be described using the following terms: Principal axis Principal focus, or focal point Focal length The principal axis is defined as: A line which passes through the centre of a lens The principle focus, or focal point, is defined as: The point at which rays of light travelling parallel to the principal axis intersect the principal axis and converge Focal length is defined as: The distance between the centre of the lens and the principle focus

Converging Lens - Real Image

Lenses can be used to form images of objects placed in front of them The location (and nature) of the image can be found by drawing a ray diagram: Diagram showing the formation of a real image by a lens 1)Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line 2)Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly towards the principal focus 3)The image is found at the point where the above two rays meet The above diagram shows the image that is formed when the object is placed at a distance between one focal length (f) and two focal lengths (2f) from the lens In this case, the image is: Real Enlarged Inverted The following diagram shows what happens when the object is more distanced - further than twice the focal length (2f) from the lens: Diagram showing the formation of a real image by a lens with the object at distance In this case the image is: Real Diminished (smaller)Inverted If the object is placed at exactly twice the focal length (2f) from the lens: Diagram showing the formation of a real image with the object at 2f In this case the image is: Real Same size as the object Inverted

Lenz's Law

Lenz Law states: The direction of an induced potential difference always opposes the change that produces it This means that any magnetic field created by the potential difference will act so that it tries to stop the wire or magnet from moving

Properties of Liquids

Liquids have no definite shape but do have a definite volume Liquids are able to flow to take the shape of a container but they are not compressible

Longitudinal Waves

Longitudinal waves are defined as: Waves where the points along its length vibrate parallel to the direction of energy transfer For a longitudinal wave: The energy transfer is in the same direction as the wave motion They transfer energy, but not the particles of the medium They can move in solids, liquids and gases They can not move in a vacuum (since there are no particles) The key features of a longitudinal wave are where the points are: Close together, called compressions Spaced apart, called rarefactions Longitudinal waves can be seen in a slinky spring when it is moved quickly backwards and forwards Examples of longitudinal waves are: Sound waves P-waves (a type of seismic wave) Pressure waves caused by repeated movements in a liquid or gas

Representing Longitudinal Waves

Longitudinal waves are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer Drawing the lines closer together represents the compressions Drawing the lines further apart represents the rarefactions Longitudinal waves are represented as sets of lines with rarefactions and compressions

Compression & Rarefaction

Longitudinal waves consist of compression and rarefactions: A compression is a region of higher density i.e. a place where the molecules are bunched together A rarefaction is a region of lower density i.e. a place where the molecules are spread out Sound is a longitudinal wave consisting of compressions and rarefactions - these are areas where the pressure of the air varies with the wave These compressions and rarefactions cause changes in pressure, which vary in time with the waveTherefore, sound is a type of pressure wave When the waves hit a solid, the variations in pressure cause the surface of the solid to vibrate in sync with the sound wave When sound waves hit a solid, the fluctuating pressure causes the solid to vibrate

Electrical Hazards

Mains electricity is potentially lethal - potential differences as small as 50 volts can pose a serious hazard to individuals The risk of electrocution is indicated by hazard signs but other risks which would not be signposted are listed below Common hazards include: Damaged Insulation - If someone touches an exposed piece of wire, they could be subjected to a lethal shock Overheating of cables - Passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires Damp conditions - If moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk Excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply - If plugs or sockets become overloaded due to plugging in too many components the heat created can cause fires

Mains Electricity

Mains electricity is the electricity generated by power stations and transported around the country through the National Grid Everyone connects to the mains when plugging in an appliance such as a phone charger or kettle Mains electricity is an alternating current (a.c.) supply In the UK, the domestic electricity supply has a frequency of 50 Hz and a potential difference of about 230 VA frequency of 50 Hz means the direction of the current changes back and forth 50 times every second Mains electricity, being an alternating current, does not have positive and negative sides to the power source The equivalent to positive and negative are called live and neutral and these form either end of the electrical circuit

Safety Considerations

Make sure never to touch the heater whilst it is on, otherwise, it could burn skin or set something on fire Run any burns immediately under cold running water for at least 5 minutes Allow time for all the equipment, including the heater, wire and block to cool before packing away the equipment Keep water away from all electrical equipment Wear eye protection if using a beaker of hot water

Changes of State (Melting & Freezing)

Melting occurs when a solid turns into a liquid Freezing occurs when a liquid turns into a solid

Determining Resistance in Parallel Extended

More generally, to determine the combined resistance of any combination of two resistors, you must use the equation: The above equation is not the same as R = R1 + R2 - a common, incorrect simplification that is made To calculate the resistance: First find the value of 1/R (by adding 1/R1 + 1/R2) Next find the value of R by using the reciprocal button on your calculator (labelled either x-1 or 1/x, depending on your calculator)

Heating

Most homes in cold countries are fitted with central heating systems These utilise natural gas in order to heat up water which can be pumped around radiators throughout the home

Energy from the Sun

Most of our energy resources on the Earth come from the Sun: The Sun heats up the atmosphere, creating wind and producing waves Water evaporated by the Sun falls as rain, filling up reservoirs Plants grown using sunlight form the basis for fuels - both biofuels and fossil fuels Some forms of energy, however, do not come from the Sun These include: Geothermal - this comes from heat produced in the Earth's core Nuclear - this comes from elements which make up a small proportion of the Earth's crust Tidal - this comes (mainly) from the gravitational attraction of the Moon

Use the formula triangle to help you rearrange the equation

Multiplying force and distance produces units of newton-metres (N m)Work is measured in Joules (J) This leads to a simple conversion: 1 J = 1 N m Therefore, the number of Joules is equal to the number of newton-metres, making conversions between the units very straightforward, for example: 1000 J = 1000 N m One Joule is equal to the work done by a force of one newton acting through one metre Whenever any work is done, energy is transferred mechanically from one store to another The amount of energy transferred (in joules) is equal to the work done (also in joules) energy transferred (J) = work done (J) If a force acts in the direction that an object is moving, then the object will gain energy (usually to its kinetic energy store) If the force acts in the opposite direction to the movement then the object will lose energy (usually to the thermal energy store of the surroundings ie dissipated as heat) Therefore: W = fd = ΔE

Hydroelectric Dams disadvantages

Need to flood valleys to build which destroys habitats, towns and villages The pumping systems can release large amounts of greenhouse gases

Calculations Using Newton's Second Law

Newton's second law can be expressed as an equation: F = ma Where: F = resultant force on the object in Newtons (N)m = mass of the object in kilograms (kg)a = acceleration of the object in metres per second squared (m/s2) The force and the acceleration act in the same direction

What does Newton's second law of motion state?

Newton's second law of motion states: The acceleration of an object is proportional to the resultant force acting on it and inversely proportional to the object's mass Newton's second law explains the following important principles: An object will accelerate (change its velocity) in response to a resultant force The bigger this resultant force, the larger the acceleration For a given force, the greater the object's mass, the smaller the acceleration experienced

Nuclear Charge

Nuclear charge is normally stated as the relative charge of the nucleus The term 'relative' refers to the charge of the particle divided by the charge of the proton The proton number is the number of protons in a nucleus Since nuclei are made up of only protons and neutrons, the proton number determines the relative charge on a nucleus

Positive & Negative Charges

Objects can be given one of two types of electric charge: Positive Negative When two charged objects are brought close together, there will be a force between those objects Like charges repel; opposite charges attract Remember: Opposite charges attract Like charges repel Electric charge is measured in units called coulombs (C)

Motion of Falling Objects (with air resistance)

Objects falling through fluids (fluids are liquids or gases) in a uniform gravitational field, experience two forces: Weight (due to gravity)Friction (such as air resistance) A skydiver jumping from a plane will experience: A downward acting force of weight (mass × acceleration of freefall) An upward acting force of air resistance (frictional forces always oppose the direction of motion) Initially, the upwards air resistance is very small because the skydiver isn't falling very quickly Therefore, there are unbalanced forces on the skydiver initially As the skydiver speeds up, air resistance increases, eventually growing large enough to balance the downwards weight force Once air resistance equals weight, the forces are balanced This means there is no longer any resultant force Therefore, the skydiver's acceleration is zero - they now travel at a constant speed This speed is called their terminal velocity When the skydiver opens the parachute, the air resistance increases This is due to the increased surface area of the parachute opening The upward force of air resistance on the skydiver increases, slowing the acceleration of the skydivers fall The skydiver decelerates Eventually, the forces balance out again, and a new slower terminal velocity is reached

Electric Field Patterns (Extended)

Objects in an electric field will experience an electric force Since force is a vector, the direction of this force depends on whether the charges are the same or opposite The force is either attractive or repulsive If the charges are the same (negative and negative or positive and positive), this force will be repulsive and the second charged object will move away from the charge creating the field If the charges are the opposite (negative and positive), this force will be attractive and the second charged object will move toward the charge creating the field Electric field lines show force direction and force strength The size of the force depends on the strength of the field at that point This means that the force becomes: Stronger as the distance between the two charged objects decreases Weaker as the distance between the two charged objects increases The relationship between the strength of the force and the distance applies to both the force of attraction and force of repulsion Two negative charges brought close together will have a stronger repulsive force than if they were far apart

Optical Fibres

Optical fibres (visible light or infrared) are used for cable television and high-speed broadband This is because glass is transparent to visible light and some infrared Also, visible light and short wavelength infrared can carry high rates of data due to their high frequency Optical fibres use visible light or infrared for transmitting cable television and high-speed broadband signals

Orbital Distance, Speed and Duration (Venus)

Orbital distance/million km- 108.2 Orbital Speed/km/s- 35.0 Orbital duration/days or years- 225 days

Data for planets in our Solar System (Venus)

Orbital distance/million km- 108.2 Orbital duration/ days or years- 225 days Density/kg/m3- 5243 Surface temperature/°C- 460 Uniform surface gravitational field strength/ N/kg- 8.9

Data for planets in our Solar System (Saturn)

Orbital distance/million km- 1433.5 Orbital duration/ days or years- 29.5 years Density/kg/m3- 687 Surface temperature/°C- -180 Uniform surface gravitational field strength/ N/kg- 9.0

Orbital Distance, Speed and Duration (Earth)

Orbital distance/million km- 149.6 Orbital Speed/km/s- 29.8 Orbital duration/days or years- 365 days

Data for planets in our Solar System (Earth)

Orbital distance/million km- 149.6 Orbital duration/ days or years- 365 days Density/kg/m3- 5514 Surface temperature/°C- 20 Uniform surface gravitational field strength/ N/kg- 9.8

Orbital Distance, Speed and Duration (Mars)

Orbital distance/million km- 227.9 Orbital Speed/km/s- 24.1 Orbital duration/days or years- 687 days

Data for planets in our Solar System (Mars)

Orbital distance/million km- 227.9 Orbital duration/ days or years- 687 days Density/kg/m3- 3933 Surface temperature/°C- -23 Uniform surface gravitational field strength/ N/kg- 3.7

Orbital Distance, Speed and Duration (Uranus)

Orbital distance/million km- 2872.5 Orbital Speed/km/s- 6.8 Orbital duration/days or years- 75 years

Data for planets in our Solar System (Uranus)

Orbital distance/million km- 2872.5 Orbital duration/ days or years- 75 years Density/kg/m3- 1271 Surface temperature/°C- -210 Uniform surface gravitational field strength/ N/kg- 8.7

Data for planets in our Solar System (Neptune)

Orbital distance/million km- 4495.1 Orbital duration/ days or years- 165 years Density/kg/m3- 1638 Surface temperature/°C- -220 Uniform surface gravitational field strength/ N/kg- 11.0

Orbital Distance, Speed and Duration (Mercury)

Orbital distance/million km- 57.9 Orbital Speed/km/s- 47.9 Orbital duration/days or years- 88 days

Data for planets in our Solar System (Mercury)

Orbital distance/million km- 57.9 Orbital duration/ days or years- 88 days Density/kg/m3- 5427 Surface temperature/°C- 350 Uniform surface gravitational field strength/ N/kg- 3.7

Orbital Distance, Speed and Duration (Jupiter)

Orbital distance/million km- 778.6 Orbital Speed/km/s- 13.1 Orbital duration/days or years- 11.9 years

Data for planets in our Solar System (Jupiter)

Orbital distance/million km- 778.6 Orbital duration/ days or years- 11.9 years Density/kg/m3- 1326 Surface temperature/°C- -120 Uniform surface gravitational field strength/ N/kg- 23.1

Elliptical Orbits

Orbits of planets, minor planets and comets are elliptical An ellipse is just a 'squashed' circle Planets, minor planets and comets have elliptical orbits However, the Sun is not at the centre of an elliptical orbit This is only the case when the orbit is approximately circular Planets and comets travel in elliptical orbits, but the Sun is not at the centre of these orbits

Worked Example A wave in a pond has a speed of 0.15 m/s and a time period of 2 seconds. Calculate: a) The frequency of the wave b) The wavelength of the wave

Part (a) Step 1: List the known quantities Time period, T = 2 s Step 2: Write out the equation relating time period and frequency Step 3: Rearrange for frequency, f, and calculate the answer f = 1 ÷ T = 1 ÷ 2 Frequency, f = 0.5 Hz Part (b) Step 1: List the known quantities Wave speed, v = 0.15 m/s Frequency, f = 0.5 Hz Step 2: Write out the wave speed equation v = f × λ Step 3: Rearrange the equation to calculate the wavelength λ = v ÷ f Step 4: Use the frequency you calculated in part (a) and put the values into the equation λ = 0.15 ÷ 0.5 Wavelength, λ = 0.30 m

Worked Example A car salesman says that his best car has a mass of 900 kg and can accelerate from 0 to 27 m/s in 3 seconds. Calculate: a) The acceleration of the car in the first 3 seconds. b) The force required to produce this acceleration.

Part (a) Step 1: List the known quantities Initial velocity = 0 m/s Final velocity = 27 m/s Time, t = 3 s Step 2: Calculate the change in velocity change in velocity = Δv = final velocity − initial velocity Δv = 27 − 0 = 27 m/s Step 3: State the equation for acceleration Step 4: Calculate the acceleration a = 27 ÷ 3 = 9 m/s2 Part (b) Step 1: List the known quantities Mass of the car, m = 900 kg Acceleration, a = 9 m/s2 Step 2: Identify which law of motion to apply The question involves quantities of force, mass and acceleration, so Newton's second law is required: F = ma Step 3: Calculate the force required to accelerate the car F = 900 × 9 = 8100 N

Tora is training for a cycling tournament. The speed-time graph below shows her motion as she cycles along a flat, straight road. (a) In which section (A, B, C, D, or E) of the speed-time graph is Tora's acceleration the largest? (b) Calculate Tora's acceleration between 5 and 10 seconds.

Part (a) Step 1: Recall that the slope of a speed-time graph represents the magnitude of acceleration The slope of a speed-time graph indicates the magnitude of acceleration Therefore, the only sections of the graph where Tora is accelerating is section B and section D Sections A, C, and E are flat - in other words, Tora is moving at a constant speed (i.e. not accelerating) Step 2: Identify the section with the steepest slope Section D of the graph has the steepest slope Hence, the largest acceleration is shown in section D Part (b) Step 1: Recall that the gradient of a speed-time graph gives the acceleration Calculating the gradient of a slope on a speed-time graph gives the acceleration for that time period Step 2: Draw a large gradient triangle at the appropriate section of the graph A gradient triangle is drawn for the time period between 5 and 10 seconds below: Step 3: Calculate the size of the gradient and state this as the acceleration The acceleration is given by the gradient, which can be calculated using: acceleration = gradient = 5 ÷ 5 = 1 m/s2 Therefore, Tora accelerated at 1 m/s2 between 5 and 10 seconds

Worked Example Small water waves are created in a ripple tank by a wooden bar. The wooden bar vibrates up and down hitting the surface of the water. The diagram below shows a cross-section of the ripple tank and water. Identify the letter which shows: a) The amplitude of a water wave. b) The wavelength of the water wave.

Part (a) Step 1: Recall the definition of amplitude Amplitude = The distance from the undisturbed position to the peak or trough of a wave Step 2: Mark the undisturbed position on the wave This is the centre of the wave Step 3: Identify the arrow between the undisturbed position and a peak The amplitude is shown by arrow D Part (b) Step 1: Recall the definition of wavelength Wavelength = The distance from one point on the wave to the same point on the next wave Step 2: Draw lines on each horizontal arrow This helps to identify the points on the wave the arrows are referring to Step 3: Identify the arrow between two of the same points on the wave The wavelength is shown by arrow C

Correcting Long-Sightedness

People who are long-sighted have eyes that are 'too small' This means they cannot clearly see things that are close, and can only clearly see things that are far away This is because the eye refracts the light rays and they are brought to a focus beyond the retina In other words, the focus point is behind the retina at the back of the eye This can be corrected by using a convex or converging lens

Uses of Permanent Magnets

Permanent magnets are usually (but not always) made from steel They tend to stay magnetised Permanent magnets have many uses including Compasses: for thousands of years humans have used compasses for navigation, since the needle always points north School lab experiments; the magnets used in school science demonstrations are permanent magnets Toys; toy trains trucks often have magnets which attach the carriages or trailers to the engine or cab Fridge magnets; these are made either of flexible magnetic material or by sticking a magnet to the back of something

Examples of other radiation detectors include:

Photographic film (often used in badges) Ionisation chambers Scintillation counters Spark counters

Plotting Magnetic Field Lines (using iron fillings)

Place a piece of paper on top of the magnet Gently sprinkle iron filings on top of the paper Now carefully tap the paper to allow the iron filings to settle on the field lines Iron filings can be used to plot a magnetic field Place the magnet on top of a piece of paper Draw a dot at one end of the magnet (near its corner) Place a plotting compass next to the dot, so that one end of the needle of the compass points towards the dot Use a pencil to draw a new dot at the other side of the compass needle Now move the compass so that it points towards the new dot, and repeat the above process Keep repeating until you have a chain of dots going from one end of the magnet to the other. Then remove the compass, and link the dots using a smooth curve - the magnetic field line The direction of the field line is the same as the direction of the plotting compass You can now repeat the whole process several times to create several other magnetic field lines Compasses can be used to plot the magnetic field around a bar magnet

Measuring Density (Regular and irregular shaped objects)

Purpose- objects to use to determine the density of

Investigating Specific Heat Capacity (Equipment list) Voltmeter

Purpose- to determine the potential difference through the heater Resolution = 0.1V

Investigating Specific Heat Capacity (Equipment list) Immersion heater

Purpose- to heat the substance

Equipment (Flasks painted different colours- black, dull grey, white, silver)

Purpose- to investigate the heat loss of the different colours

Measuring Density (A 30cm ruler)

Purpose- to measure objects up to 30cm in length Resolution- 1mm

Equipment (4 Thermometers)

Purpose- to measure the temperature of the water Resolution- 1°C

Investigating Specific Heat Capacity (Equipment list) Stopwatch

Purpose- to measure the time taken for the substance to heat up by a certain temperature Resolution = 0.01 s

Measuring Density (Measuring cylinders)

Purpose- to measure the volume of liquid

Equipment (Stopwatch)

Purpose- to record the time it takes for water to cool Resolution- 0.01s

Investigating Specific Heat Capacity (Equipment list) Power supply

Purpose- to supply power to the heater

Measuring the Thickness of Materials

Radiation can be used for tracing and gauging thickness Mostly commonly this is beta particles As a material moves above a beta source, the particles that are able to penetrate it can be monitored using a detector If the material gets thicker, more particles will be absorbed, meaning that less will get throughIf the material gets thinner the opposite happens This allows the machine to make adjustments to keep the thickness of the material constant Beta particles can be used to measure the thickness of thin materials such as paper, cardboard or aluminium foil Beta radiation is used because it will be partially absorbed by the material If alpha particles were used all of them would be absorbed and none would get through If gamma were used almost all of it would get through and the detector would not be able to sense any difference if the thickness were to change

Uses of Radiation

Radiation is used in a number of different ways: 1)Medical procedures including diagnosis and treatment of cancer 2)Sterilising food (irradiating food to kill bacteria) 3)Sterilising medical equipment (using gamma rays) 4)Determining the age of ancient artefacts 5)Checking the thickness of materials 6)Smoke detectors (alarms) The properties of the different types of radiation determine which one is used in a particular application

Radio Waves

Radio waves can be used to transmit signals over short distances Terrestrial (local) television signals, radio station transmissions and Bluetooth all work using radio waves Radio station signals are transmitted at a longer wavelength than terrestrial television signals In hilly areas it may be possible to receive radio signals but not receive terrestrial television signals This is because radio signals are more prone to diffraction around the hills Radio signals tend to have wavelengths of around a kilometre, so the radio signals are more likely to have wavelength similar to the size of the hill This leads to diffraction, so radio signals can reach locations not in the line-of-sight of the transmitter, whereas TV signals are not diffracted Bluetooth uses radio waves instead of wires or cables to transmit information between electronic devices, such as phones and speakers, over short distances Bluetooth signals tend to have shorter wavelengths than radio station or television signals This enables high rates of data transmission, but can only be used over a short distance (for example, within a household) This means they can pass through walls but the signal is significantly weakened on doing so Radio signals diffract around hills because they are a similar wavelength to the hill

Geothermal Energy

Radioactive elements deep in the Earth release energy as they decay, this geothermal energy heats up the rocks, sometimes to a high temperature Water can be poured into shafts below the Earth's surface which is heated by the rocks and returned via another shaft as steam or hot water Steam can be used to turn a turbine and generate electricity, and hot water can be used to heat homes

Diagnosis and Treatment of Cancer

Radiotherapy is the name given to the treatment of cancer using radiation (Chemotherapy is treatment using chemicals) Although radiation can cause cancer, it is also highly effective at treating it Radiation can kill living cells. Some cells, such as bacteria and cancer cells, are more susceptible to radiation than others Beams of gamma rays are directed at the cancerous tumour Gamma rays are used because they are able to penetrate the body, reaching the tumour The beams are moved around to minimise harm to healthy tissue whilst still being aimed at the tumour A tracer is a radioactive isotope that can be used to track the movement of substances, like blood, around the body A PET scan can detect the emissions from a tracer to diagnose cancer and determine the location of a tumour

Natural Sources

Radon gas (in the air) Airborne radon comes from the ground This is from the natural decay of uranium in rocks and soil The gas is tasteless, colourless and oderless but it not generally a health issue Rocks and Buildings Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground Uranium decays into radon gas, which is an alpha emitter This is particularly dangerous if inhaled into the lungs in large quantities Natural radioactivity can be found in building materials, including decorative rocks, stone and brick Cosmic rays from space The sun emits an enormous number of protons every second Some of these enter the Earth's atmosphere at high speeds When they collide with molecules in the air, this leads to the production of gamma radiation Other sources of cosmic rays are supernovae and other high energy cosmic events Carbon-14 in biological material All organic matter contains a tiny amount of carbon-14 Living plants and animals constantly replace the supply of carbon in their systems hence the amount of carbon-14 in the system stays almost constant Radioactive material in food and drink Naturally occurring radioactive elements can get into food and water since they are in contact with rocks and soil containing these elements Some foods contain higher amounts such as potassium-40 in bananas However, the amount of radioactive material is minuscule and is not a cause for concern

Investigating Reflection

Reflection can be shown by the waves hitting a plane (straight) surface, such as a wall or mirror

Reflection

Reflection occurs when: A wave hits a boundary between two media and does not pass through, but instead stays in the original medium The law of reflection states: The angle of incidence = The angle of reflection When waves hit an object, such as a barrier, they can be reflected: When waves reflect off a barrier, the angle of reflection, r, is equal to the angle of incidence, i

Investigating Refraction

Refraction can be shown by placing a glass block in the tank The glass block should sit below the surface of the water and cover only some of the tank floor The depth of water becomes shallower here the glass block is placedSince speed depends on depth, the ripples slow down when travelling over the block This is a good model of refraction showing how waves slow down when passing from deep water into shallow water When water waves travel from deep areas to shallow areas they slow down

Refraction of Light

Refraction occurs when light passes a boundary between two different transparent media At the boundary, the rays of light undergo a change in direction The direction is taken as the angle from a hypothetical line called the normal This line is perpendicular to the surface of the boundaries and is usually represented by a straight dashed or dotted line The change in direction depends on which media the light rays pass between: From less dense to more dense (e.g air to glass), light bends towards the normal From more dense to less dense (e.g. glass to air), light bends away from the normal When passing along the normal (perpendicular) the light does not bend at all How to construct a ray diagram showing the refraction of light as it passes through a rectangular block The change in direction occurs due to the change in speed when travelling in different substances When light passes into a denser substance the rays will slow down, hence they bend towards the normal The only properties that change during refraction are speed and wavelength - the frequency of waves does not change Different frequencies account for different colours of light (red has a low frequency, whilst blue has a high frequency) When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change

Refraction

Refraction occurs when: A wave passes a boundary between two different transparent media and undergoes a change in direction When waves enter a different medium, their speed can change This effect is called refraction, and it can have two other effects: The wavelength of the waves can increase or decrease The waves can change direction Waves can change direction when moving between materials with different densities If the waves slow down, the waves will bunch together, causing the wavelength to decrease The waves will also start to turn slightly towards the normal If the waves speed up then they will spread out, causing the wavelength to increase The waves will also turn slightly away from the normal

Consequences of Ohm's Law

Resistors are used in circuits to control either The current in branches of the circuit (through certain components) The potential difference across certain components This is due to the consequences of Ohm's Law The current in an electrical conductor decreases as its resistance increases (for a constant p.d.) The p.d. across an electrical conductor increases as its resistance increases (for a constant current)

How to calculate resultant forces?

Resultant forces can be calculated by adding or subtracting all of the forces acting on the object Forces working in opposite directions are subtracted from each other Forces working in the same direction are added together If the forces acting in opposite directions are equal in size, then there will be no resultant force - the forces are said to be balanced

Investigating Waves with a Ripple Tank

Ripple tanks are commonly used in experiments to demonstrate the following properties of water waves: Reflection at a plane surface Refraction due to a change in speed caused by a change in depth Diffraction due to a gap Diffraction due to an edge Reflection, refraction and diffraction can be demonstrated using a ripple tank

Measuring Wave Speed in Water

Ripples on water surfaces are used to model transverse waves The speed of these water waves can be measured Creating ripples in water 1)Choose a calm flat water surface such as a lake or a swimming pool 2)Two people stand a few metres apart using a tape measure to measure this distance 3)One person counts down from three and then disturbs the water surface (using their hand, for example) to create a ripple 4)The second person then starts a stopwatch to time how long it takes for the first ripple to get to them 5)The experiment is then repeated 10 times and an average value for the time is calculated 6)The average time and distance can then be used to calculate the wave speed using the equation: AVERAGE SPEED = DISTANCE MOVED TIME TAKEN

Magnetic Fields

Similarly, alpha and beta particles are deflected by magnetic fields whilst they are moving They are deflected in opposite directions due to their opposite charges Alpha and Beta particles can also be deflected by magnetic fields

Age of the Universe

Since Hubble's Law states that H0 = v d It can be rearranged to show that 1 = d H0 v Hubble's law shows that the further away a star is from the Earth, the faster it is moving away from us A key aspect of Hubble's law is that the furthest galaxies appear to move away the fastest The gradient of the graph can be used to find the Age of the Universe When the distance equals zero, this represents all the matter in the Universe being at a single point This is the singularity that occurred at the moment of the Big Bang The units of the gradient are per second (the same as the units of the Hubble Constant) By taking the reciprocal, or, 1 the units will become seconds H0 Therefore the reciprocal of the gradient represents time and gives the amount of time which the Universe has been expanding for Astronomers have used this formula to estimate the age of the Universe at about 13.7 billion years

Nuclear Fusion

Small nuclei can react to release energy in a process called nuclear fusion Nuclear fusion is defined as: When two light nuclei join to form a heavier nucleus This process requires extremely high temperatures to maintain This is why nuclear fusion has proven very hard to reproduce on Earth Stars use nuclear fusion to produce energy In most stars, hydrogen atoms are fused together to form helium and produce lots of energy Two hydrogen nuclei are fusing to form a helium nuclei The energy produced during nuclear fusion comes from a very small amount of the particle's mass being converted into energy Albert Einstein described the mass-energy equivalence with his famous equation: E = m × c2 Where: E = energy released from fusion in Joules (J) m = mass converted into energy in kilograms (kg) c = the speed of light in metres per second (m/s) Therefore, the mass of the product (fused nucleus) is less than the mass of the two original nuclei This is because the remaining mass has been converted into energy which is released when the nuclei fuse The amount of energy released during nuclear fusion is huge: The energy from 1 kg of hydrogen that undergoes fusion is equivalent to the energy from burning about 10 million kilograms of coal An example of a nuclide equation for fusion is: + energy Where: is deuterium (isotope of hydrogen with 1 proton and 1 neutron) is hydrogen (with one proton) is an isotope with helium (with two protons and one neutron)

Advantages to using solar cells

Solar energy is a renewable resource In many places on Earth sunlight is a reliable energy resource (this means that the sun shines most of the time) Solar farms produce no greenhouse gases or pollution Solar energy can be generated in remote places where they don't have electricity For example to power solar street signs in rural areas

Solar Panels

Solar panels transfer energy from sunlight to the thermal store of the solar panels which is used to heat water in the pipes Solar panels can be used to warm domestic water supplies This can reduce the cost of producing hot water since it is heated partially by the solar panels Solar furnaces consist of large curved mirrors that focus the sun's rays on to a small area These can be used to boil water, generating enough steam to turn turbines and generate electricity in a power station

Properties of Solids

Solids have a definite shape and a definite volume Solids cannot flow and are not compressible

Radioactive Decay

Some atomic nuclei are unstable This is because of an imbalance in the forces within the nucleus Forces exist between the particles in the nucleus This is commonly due to the nucleus have too many protons or neutrons Carbon-14 is an isotope of carbon which is unstable It has two extra neutrons compared to stable carbon-12 Carbon-12 is stable, whereas carbon-14 is unstable. This is because carbon-14 has two extra neutrons Some isotopes are unstable because of their large size or because they have too many or too few neutrons Unstable nuclei can emit radiation to become more stable Radiation can be in the form of a high energy particle or wave Unstable nuclei decay by emitting high energy particles or waves As the radiation moves away from the nucleus, it takes some energy with it This reduces the overall energy of the nucleus This makes the nucleus more stable The process of emitting radiation is called radioactive decay Radioactive decay is a random processThis means it is not possible to know exactly when a particular nucleus will decay It cannot be predicted when a particular unstable nucleus will decay This is because radioactive decay is a random process, this means that: There is an equal probability of any nucleus decaying It cannot be known which particular nucleus will decay next It cannot be known at what time a particular nucleus will decay The rate of decay is unaffected by the surrounding conditions It is only possible to estimate the probability of a nuclei decaying in a given time period Therefore, the emission of radiation is: Spontaneous Random in direction

Total Internal Reflection

Sometimes, when light is moving from a denser medium towards a less dense one, instead of being refracted, all of the light is reflected This phenomenon is called total internal reflection Total internal reflection (TIR) occurs when: The angle of incidence is greater than the critical angle and the incident material is denser than the second material Therefore, the two conditions for total internal reflection are: The angle of incidence > the critical angle The incident material is denser than the second material Critical angle and total internal reflection Total internal reflection is utilised in: Optical fibres e.g. endoscopes Prisms e.g. periscopes

Transmission of Sound

Sound waves that can be transmitted as a digital or analogue signal Signals for speech or music are made up of varying frequencies In order to make out the information clearly, the signal needs to be transmitted with as little interference as possible The signal goes is converted both before transmission and after being received Before transmission: the signal is converted from analogue to digital After being received: the signal is converted from digital to analogue

Name an example and explain of everyday life impulse

Standing under an umbrella when it is raining, compared to hail (frozen water droplets) When rain hits an umbrella, the water droplets tend to splatter and fall off it and there is only a very small change in momentum However, hailstones have a larger mass and tend to bounce back off the umbrella, creating a greater change in momentum Therefore, the impulse on an umbrella is greater in hail than in rain This means that more force is required to hold an umbrella upright in hail compared to rain

Apparatus to investigate the specific heat capacity of the aluminium block

Start by assembling the apparatus, placing the heater into the top of the block Measure the initial temperature of the aluminium block from the thermometer Turn on the power supply and start the stopwatch Whilst the power supply is on, the heater will heat up the block. Take several periodic measurements, eg. every 1 minute of the voltage and current from the voltmeter and ammeter respectively, calculating an average for each at the end of the experiment up to 10 minutes Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools Monitor the thermometer and record the final temperature reached for the block

Liquid

State- Liquid Density- Medium Arrangement of particles- Randomly arranged Movement of particles- Move around each other Energy of particles- Greater energy

Solid

State- Solid Density- High Arrangement of particles- Regular pattern Movement of particles- Vibrate around a fixed position Energy of particles- Low energy

Thermal Expansion in Terms of Particle (Gases)

State- gases Expansion- expand significantly (because the high energy molecules have enough energy to completely overcome the intermolecular forces of attraction holding them together)

Thermal Expansion in Terms of Particle (Liquids)

State- liquid Expansion- expand more than solids (because the molecules have enough energy to partially overcome the intermolecular forces of attraction holding them together)

Thermal Expansion in Terms of Particle (Solids)

State- solid Expansion- expand slightly (because the low energy molecules cannot overcome the intermolecular forces of attraction holding them together)

Worked Example Calculate the magnitude and direction of the resultant force in the diagram below.

Step 1: Add up all of the forces directed to the right 4 N + 8 N = 12 N Step 2: Subtract the forces on the right from the forces on the left 14 N - 12 N = 2 N Step 3: Evaluate the direction of the resultant force The force to the left is greater than the force to the right therefore the resultant force is directed to the left Step 4: State the magnitude and direction of the resultant force The resultant force is 2 N to the left

Worked Example Explain the features of the solar panel that help it heat the water efficiently

Step 1: Describe how thermal radiation arrives at the water: The thermal radiation (infrared) is able to pass through the glass sheet The black metal backing sheet absorbs the thermal radiation (sunlight)Being metal (an excellent conductor) it then conducts it into the copper pipes The copper pipes (also metal) then conduct the heat into the water Step 2: Describe how the heat is trapped inside the solar panel (making it more efficient): The insulated material reduces the conduction of heat through the back of the panel, decreasing heat loss The glass also traps air which is a good insulator This prevents heat loss by conduction from the front of the panel It also prevents heat loss by convection (due to the air being trapped)

Worked Example The diagram below shows a toy duck bobbing up and down on top of the surface of some water, as waves pass it underneath. Explain how the toy duck demonstrates that waves do not transfer matter.

Step 1: Identify the type of wave The type of wave on the surface of a body of water is a transverse wave This is because the duck is moving perpendicular to the direction of the wave Step 2: Describe the motion of the toy duck The plastic duck moves up and down but does not travel with the wave Step 3: Explain how this motion demonstrates that waves do not transfer matter Both transverse and longitudinal waves transfer energy, but not the particles of the medium This means when a wave travels between two points, no matter actually travels with it, the points on the wave just vibrate back and forth about fixed positions Objects floating on the water simply bob up and down when waves pass under them, demonstrating that there is no movement of matter in the direction of the wave, only energy

Worked Example A car moving at speed begins to apply the brakes. The brakes of the car apply a force of 500 N which brings it to a stop after 23 m. Calculate the work done by the brakes in stopping the car.

Step 1: List the known quantities Distance, d = 23 m Force, F = 500 N Step 2: Write out the equation relating work, force and distance W = F × d Step 3: Calculate the work done on the car by the brakes W = 500 × 23 = 11 500 J

Steps to calculate density

Step 1: List the known quantities Mass of slab, m = Volume of slab, V = Step 2: Write out the equation for density p=m/V Step 3: Substitute in values ρ = 73 ÷ 0.017 = 4294 kg/m3 Step 4: Round the answer to two significant figures ρ = 4300 kg/m3

Worked Example A man of mass 70 kg climbs a flight of stairs that is 3 m higher than the floor. Gravitational field strength is approximately 9.81 N/kg. Calculate the energy transferred to his gravitational potential energy store.

Step 1: List the known quantities Mass of the man, m = 70 kg Gravitational field strength, g = 9.81 N/kg Height, h = 3 m Step 2: Write down the equation for gravitational potential energy ΔEP = mgΔh Step 3: Calculate the gravitational potential energy ΔEP = 70 × 9.81 × 3 = 2060 J

Worked Example Calculate the kinetic energy stored in a vehicle of mass 1200 kg moving at a speed of 27 m/s.

Step 1: List the known quantities Mass of the vehicle, m = 1200 kg Speed of the vehicle, v = 27 m/s Step 2: Write down the equation for kinetic energy EK = ½ mv2 Step 3: Calculate the kinetic energy EK = ½ × 1200 × (27)2 = 437 400 J Step 4: Round the final answer to 2 significant figures EK = 440 000 J

Worked Example A ray of light enters a glass block of refractive index 1.53 making an angle of 15° with the normal before entering the block. Calculate the angle it makes with the normal after it enters the glass block.

Step 1: List the known quantities Refractive index of glass, n = 1.53 Angle of incidence, i = 15° Step 2: Write the equation for Snell's Law Step 3: Rearrange the equation and calculate sin (r) Step 4: Find the angle of refraction (r) by using the inverse sin function r = sin-1 (0.1692) = 9.7 = 10°

Worked Example An electric motor is used to lift a weight. The diagram represents the energy transfers in the motor. How much energy is wasted?

Step 1: State the conservation of energy Energy cannot be created or destroyed, it can only be transferred from one store to another This means that: Total energy in = Useful energy out + Wasted energy Step 2: Rearrange the equation for the wasted energy Wasted energy = Total energy in - Useful energy out Step 3: Substitute the values from the diagram 500 - 120 = 380 J

Worked Example The diagram shows a car and a van, just before and just after the car collided with the van, which is initially at rest. Use the idea of conservation of momentum to calculate the velocity of the van when it is pushed forward by the collision.

Step 1: State the principle of conversation of momentum In a closed system, the total momentum before an event is equal to the total momentum after the event Step 2: Calculate total momentum before the collision p = mv Momentum of the car: p = 990x 10 = 9900 kg m/s Momentum of the van: the van is at a rest therefore v = 0 m/s and p = 0kg m/s Step 3: Calculate the momentum after the collision Momentum of the car: p = 990 x 2 = 1980 kg m/s Momentum of the van: p = 4200 x v Total momentum after: P after = 1980 + 4200v kg m/s Step 4: Rearrange the conversation of momentums equation for the velocity of the van P before = P after 9900 = 1980 + 4200v 9900 - 1980 = 4200v v = 9900 - 1980/ 4200 = 1.9m/s

Worked Example An electric motor has an efficiency of 35 %. It lifts a 7.2 kg load through a height of 5 m in 3 s. Calculate the power of the motor.

Step 1: Write down the efficiency equation Efficiency = Power output x100 Power input Step 2: Rearrange for the power input Efficiency = Power output x100 Efficiency Step 3: Calculate the power output The power output is equal to energy ÷ time The electric motor transferred electric energy into gravitational potential energy to lift the load Gravitational potential energy = mgh = 7.2 × 9.81 × 5 = 353.16 J Power = 353.16 ÷ 3 = 117.72 W Step 4: Substitute values into power input equation Power input = 117.72 x 100 35 = 336W

Worked Example Water of mass 0.48 kg is increased in temperature by 0.7 °C. The specific heat capacity of water is 4200 J / kg °C. Calculate the amount of thermal energy transferred to the water.

Step 1: Write down the known quantities Mass, m = 0.48 kg Change in temperature, ΔT = 0.7 °C Specific heat capacity, c = 4200 J/kg °C Step 2: Write down the relevant equation ΔQ = mcΔT Step 3: Calculate the thermal energy transferred by substituting in the values Step 4: Round the answer to 2 significant figures and include the units ΔQ = 1400 J

Investigating Reflection (Evaluating the Experiment)

Systematic Errors: An error could occur if the 90° lines are drawn incorrectly Use a set square to draw perpendicular lines If the mirror is distorted, this could affect the reflection angle, so make sure there are little to no blemishes on it Random Errors: The points for the incoming and reflected beam may be inaccurately markedUse a sharpened pencil and mark in the middle of the beam The protractor resolution may make it difficult to read the angles accurately Use a protractor with a higher resolution

Evaluating the Experiment

Systematic Errors: Make sure the starting temperature of the water is the same for each material since this will cool very quickly It is best to do this experiment in pairs to coordinate starting the stopwatch and immersing the thermometer Use a data logger connected to a digital thermometer to get more accurate readings Random Errors: Make sure the hole for the thermometer isn't too big, otherwise the heat will escape through the hole Take repeated readings for each coloured flask Read the values on the thermometer at eye level, to avoid parallax error

Evaluating the Experiment

Systematic Errors: Make sure the voltmeter and ammeter are initially set to zero, to avoid zero error Random Errors: Not all the heat energy supplied from the heater will be transferred to the block, some will go into the surroundings or heat up the thermometer This means the measured value of the specific heat capacity is likely to be higher than what it actually is To reduce this effect, make sure the block is fully insulated A joulemeter could be used to calculate energy directly This would eliminate errors from the voltmeter, ammeter and the stopwatch Make sure the temperature value is read at eye level from the thermometer, to avoid parallax error The experiment can also be repeated with a beaker of water of equal mass, the water should heat up slower than the aluminium block

The Earth's Orbit

The Earth orbits the Sun once in approximately 365 days This is 1 year The combination of the orbiting of the Earth around the Sun and the Earth's tilt creates the seasons Seasons in the Northern hemisphere caused by the tilt of the Earth Over parts B, C and D of the orbit, the northern hemisphere is tilted towards the Sun This means daylight hours are more than hours of darkness This is spring and summer The southern hemisphere is tilted away from the Sun This means there are shorter days than night This is autumn and winter Over parts F, G and H of the orbit, the northern hemisphere is tilted away from the Sun The situations in both the northern and southern hemisphere are reversed It is autumn and winter in the northern hemisphere, but at the same time it is spring and summer in the southern hemisphere At C: This is the summer solstice The northern hemisphere has the longest day, whilst the southern hemisphere has its shortest day At G: This is the winter solstice The northern hemisphere has its shortest day, whilst the southern hemisphere has its longest day At A and D: Night and day are equal in both hemispheres These are the equinoxes

Day and Night

The Earth's rotation around its axis creates day and night Day is experienced by the half of the Earth's surface that is facing the Sun Night is the other half of the Earth's surface, facing away from the Sun Day and night are caused by the Earth's rotation

Rising and Setting of the Sun

The Earth's rotation on its axis makes the Sun looks like it moves from east to west At the equinoxes the Sun rises exactly in the east and sets exactly in the west Equinox (meaning 'equal night') is when day and night are approximately of equal length However, the exact locations of where the Sun rises and sets changes throughout the seasons In the northern hemisphere (above the equator): In summer, the sun rises north of east and sets north of west In winter, the sun rises south of east and sets south of west The Sun rises in the east and sets in the west. Its approximate area changes throughout the year The Sun is highest above the horizon at noon (12 pm) In the northern hemisphere, the daylight hours are longest up until roughly the 21st June This day is known as the Summer Solstice and is where the Sun is at its highest point in the sky all year The daylight hours then decrease to their lowest around 21st December This is known the Winter Solstice and is where the Sun is at its lowest point in the sky all year

Geiger-Müller tube

The Geiger-Müller tube is the most common device used to measure and detect radiation Each time it absorbs radiation, it transmits an electrical pulse to a counting machine This makes a clicking sound or displays the count rate The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing Therefore, it matters how close the tube is to the radiation source The further away from the source, the lower the count rate detected

Investigating Electrical Conductors & Insulators

The Gold-leaf Electroscope (GLE) To distinguish between conductors and insulators a Gold-leaf electroscope (GLE) can be used The gold-leaf electroscope is a device used to demonstrate charge The GLE consists of A metal plate attached to one end of a metal rod At the other end of the rod a very thin leaf of gold foil is attached The rod is held by an insulating collar inside a box with glass sides, allowing the gold leaf to both be seen and protected from draughts When the GLE is charged, the plate, rod and gold leaf have the same charge (either positive or negative) Since the rod and leaf have the same charge, they repel, and the leaf sticks out to the side When the rod and leaf are discharged (are neutral) the leaf hangs down

Brownian Motion

The Kinetic Theory of Matter, which simply says that all matter is made up of tiny particles, was discovered almost by accident The Scottish scientist Robert Brown first described the random motion of pollen grains in water, which he saw under a microscope This observation could not be explained at the time, but later it was realised that it shows that substances are made of particles which are in constant motion (hence 'kinetic') Brownian Motion: the random motion of microscopic particles when observed through a microscope Brownian motion is the random movement of particles in a liquid or a gas produced by large numbers of collisions with smaller particles which are often too small to see When small particles (such as pollen or smoke) are suspended in a liquid or gas, they can be observed through a microscope moving around in a random, erratic fashion Light, fast-moving molecules collide with larger particles, giving them a little nudge When observing Brownian Motion, even with a microscope, only the microscopic particles can be seen The pollen or smoke particles are seen to move Smaller atoms and molecules, of water or air, are still too small to be seen These light, fast-moving atoms and molecules collide with the larger microscopic particles The collisions give the particles a little nudge, causing them to change their speed and directions randomly, each time they are struck by a molecule The presence of the light, fast moving atoms and molecules is inferred from the motion of the microscopic particles Inferences such as this are an important part of scientific investigation

Moon & Earth

The Moon is a satellite around the Earth It travels around the Earth in roughly a circular orbit once a month This takes 27-28 days The Moon revolves around its own axis in a month so always has the same side facing the Earth We never see the hemisphere that is always facing away from Earth, although astronauts have orbited the Moon and satellite have photographed it The Moon shines with reflected light from the Sun, it does not produce its own light

The Sun & the Planets

The Sun lies at the centre of the Solar System The Sun is a star that makes up over 99% of the mass of the solar system There are eight planets and an unknown number of dwarf planets which orbit the Sun The gravitational field around planets is strong enough to have pulled in all nearby objects with the exception of natural satellites The gravitational field around a dwarf planet is not strong enough to have pulled in nearby objects The 8 planets in our Solar System in ascending order of the distance from the Sun are: Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Satellites There are two types of satellite: Natural Artificial Some planets have moons which orbit them Moons are an example of natural satellites Artificial satellites are man-made and can orbit any object in space The International Space Station (ISS) orbits the Earth and is an example of an artificial satellite

The Sun

The Sun lies at the centre of the Solar System The Sun is a star which makes up over 99% of the mass of the solar system The fact that most of the mass of the Solar System is concentrated in the Sun is the reason the smaller planets orbit the Sun The gravitational pull of the Sun on the planets keeps them in orbit The Sun is a medium sized star consisting of mainly hydrogen and helium It radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum Stars come in a wide range of sizes and colours, from yellow stars to red dwarfs, from blue giants to red supergiant's These can be classified according to their colour Warm objects emit infrared and extremely hot objects emit visible light as well Therefore, the colour they emit depends on how hot they are A star's colour is related to its surface temperature A red star is the coolest (at around 3000 K) A blue star is the hottest (at around 30 000 K) The colour of a star correlates to its temperature

Investigating Thermal Radiation Aims of the Experiment

The aim of the experiment is to investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface Variables: Independent variable = Colour Dependent variable = Temperature Control variables: Identical flasks (except for their colour) Same amounts of hot water Same starting temperature of the water Same time interval

Temperature & Energy of Particles

The amount of pressure that a gas exerts on its container is dependent on the temperature of the gas This is because particles gain kinetic energy as their temperature increases As the temperature of the gas decreases, the pressure on the container also decreases In 1848, Mathematician and Physicist, Lord Kelvin, recognised that there must be a temperature at which the particles in a gas exert no pressure At this temperature they must no longer be moving, and hence not colliding with their container This temperature is called absolute zero and is equal to -273 °C At absolute zero, or -273 °C, particles will have no net movement. It is therefore not possible to have a lower temperature The unit kelvin is written as K Note that there is no degree as with Celsius, which is written °C

The Gas Laws (Pressure & Temperature (Constant Volume)

The average speed of motion of molecules increases when the temperature increases (and vice versa) Since the average kinetic energy depends on their speed, the kinetic energy of the molecules also increases if its volume remains constantThe hotter the gas, the higher the average kinetic energyThe cooler the gas, the lower the average kinetic energy As the gas heats up, the molecules will travel at a higher speed They collide with the walls more often, increasing the pressure Therefore, at a constant volume, an increase in temperature increases the pressure of a gas and vice versa Diagram A shows molecules in the same volume collide with the walls of the container more as the temperature increases Diagram B shows that since the temperature is proportional to the pressure, the graph is a straight line At constant volume, an increase in the temperature of the gas increases the pressure due to more collisions on the container walls

What is the centre of gravity?

The centre of gravity of an object is the point at which the weight of the object may be considered to act For example, for a person standing upright, their centre of gravity is roughly in the middle of the body behind the navel, and for a sphere, it is at the centre For symmetrical objects with uniform density, the centre of gravity is located at the point of symmetry

Using Redshift Observations to Measure the Universe

The change in wavelength of the galaxy's starlight due to redshift can be used to find the velocity, v, with which a galaxy (or any distant object) is moving away from Earth Using an equation to compare the ratio of the expected wavelength with the observed wavelength, the velocity can be found; difference between actual wavelength and expected wavelength ______________________________________________________________________________ actual wavelength = speed of the galaxy _________________________________ speed of light This equation will not be directly examined but the idea that the velocity of distant objects can be found from the redshift seen in easily observed wavelengths is an important one

Insulation & Double Insulation

The conducting part of a wire is usually made of copper or some other metalIf this comes into contact with a person, this poses a risk of electrocution For this reason, wires are covered with an insulating material, such as rubber The conducting part of a wire is covered in an insulating material for safety Some appliances do not have metal cases and so there is no risk of them becoming electrified Such appliances are said to be double insulated, as they have two layers of insulation: Insulation around the wires themselves A non-metallic case that acts as a second layer of insulation Double insulated appliances do not require an earth wire or have been designed so that the earth wire cannot touch the metal casing

Refractive Index & Critical Angle Equation

The critical angle, c, of a material is related to its refractive index, n The relationship between the two quantities is given by the equation: sin c = _1_ n This can also be rearranged to calculate the refractive index, n: n = _1_ sin c This equation shows that: The larger the refractive index of a material, the smaller the critical angle Light rays inside a material with a high refractive index are more likely to be totally internally reflected

Electromotive Force Extended

The definition of e.m.f. can also be expressed using an equation Where: E = electromotive force (e.m.f.) (V) W = energy supplied to the charges from the power source (J) Q = charge on each charge carrier (C) In circuits the charge carriers are electrons This equation should be compared to the definition of potential difference (below) as the two are closely related

Potential Difference Extended

The definition of p.d. can also be expressed using an equation V = _W_ Q Where: V = potential difference (p.d.) (V) W = energy transferred to the components from the charge carriers (J) Q = charge on each charge carrier (C) In circuits the charge carriers are electrons This equation should be compared to the definition of e.m.f. as the two are closely related due to conservation of energy

Left Hand Rule

The direction of the force (aka the thrust) on a current carrying wire depends on the direction of the current and the direction of the magnetic field All three will be perpendicular to each other This means that sometimes the force could appear to be acting either into or out of the page The direction of the force (or thrust) can be worked out by using Fleming's left-hand rule: Fleming's left-hand rule can be used to determine directions of the force, magnetic field and current

Efficiency of Energy Transfer

The efficiency of a system is a measure of how well energy is transferred in a system Efficiency is defined as: The ratio of the useful power or energy transfer output from a system to its total power or energy transfer input If a system has high efficiency, this means most of the energy transferred is useful If a system has low efficiency, this means most of the energy transferred is wasted The overall efficiency of a typical thermal power station is approximately 30% This means that 70% of the energy produced is wasted energy Energy is used to heat water to produce steam, that turns a turbine which generates electricity At each stage of this process, energy is dissipated to the surroundings

Electromagnetic Waves

The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies The main groupings of the continuous electromagnetic (EM) spectrum are: Radio waves Microwaves Infrared Visible (red, orange, yellow, green, blue, indigo, violet) Ultraviolet X-rays Gamma rays This order is shown in the diagram below from longest wavelength (lowest frequency) to shortest wavelength (highest frequency) Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum The higher the frequency, the higher the energy of the radiation Radiation with higher energy is: Highly ionising Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays) Radiation with lower energy is: Useful for communications Less harmful to humans

Solar Cells

The energy from the Sun that falls on the Earth is transferred by radiation Mostly visible light and infrared radiation The amount of energy transferred from the Sun to the Earth each hour is equal to the energy use of the world for one year! Therefore, scientists are working hard to find methods of harnessing this energy Solar energy has a low energy density, which means large collecting devices are required Collecting solar energy is expensive (due to the equipment required) and inefficient Solar cells transfer energy from sunlight electrically producing a current, and therefore generating electrical power Solar cells, sometimes called photovoltaic cells, are made of semiconducting materials A number of cells connected together can supply electricity to homes, small-scale businesses, communication devices and satellites Energy generated can be stored in batteries for later use

Field Lines Around a Charged Conducting Sphere

The field lines around a charge conducting sphere are symmetrical, as with a point charge This is because the charges on the surface of the sphere will be evenly distributed The charges are the same, so they repel The surface is conducting, allowing them to move This field line pattern can be demonstrated using a Van der Graaff Generator One method using streamers is shown Other methods often demonstrated in schools include Small pieces of paper Polystyrene beads Aluminium foil containers

The Forces & Distances between Molecules

The forces between particles affect the state of matter This is because the magnitude of the forces affects the relative distances and motion of the particles This affects the ability of the substance to Change shape Change volume Flow The particles that make up matter include Atoms Molecules Ions Electrons

Pitch & Loudness

The frequency of a sound wave is related to its pitch Sounds with a high pitch have a high frequency (or short wavelength) Sounds with a low pitch have a low frequency (or long wavelength) The amplitude of a sound wave is related to its volume Sounds with a large amplitude have a high volume Sounds with a small amplitude have a low volume Pitch and amplitude of sound

Gamma Decay Equation

The gamma ray that is emitted has a lot of energy, but no mass or charge Here is an example of Uranium-238 undergoing gamma decay Notice that the mass number and atomic number of the unstable nuclei remains the same during the decay

Simple A.C Generators

The generator effect can be used to generate a.c in an alternator A simple alternator is a type of generator that converts mechanical energy to electrical energy in the form of alternating current An alternator is a rotating coil in a magnetic field connected to commutator rings A rectangular coil that is forced to spin in a uniform magnetic field The coil is connected to a centre-reading meter by metal brushes that press on two metal slip rings (or commutator rings)The slip rings and brushes provide a continuous connection between the coil and the meter When the coil turns in one direction: The pointer defects first one way, then the opposite way, and then back again This is because the coil cuts through the magnetic field lines and an EMF, and therefore current, is induced in the coil The pointer deflects in both directions because the current in the circuit repeatedly changes direction as the coil spins This is because the induced EMF in the coil repeatedly changes its direction This continues on as long as the coil keeps turning in the same direction The induced EMF and the current alternate because they repeatedly change direction

Gravitational Potential Energy

The gravitational potential energy, EP, of an object (also known as its gravitational store) is defined as: The energy an object has due to its height in a gravitational field This means: If an object is lifted up, energy will be transferred to its gravitational store If an object falls, energy will be transferred away from its gravitational store The GPE of an object can be calculated using the equation: ΔEP = mgΔh Where: ΔEP = change in gravitational potential energy, in Joules (J) m = mass, in kilograms (kg) g = gravitational field strength in Newtons per kilogram (N/kg) Δh = change in height in metres (m) Energy is transferred to the mass's gravitational store as it is lifted above the ground, therefore the ΔEP increases

Comparing Converging & Diverging Lenses

The image produced by a converging lens can be either real or virtual This means the image can be inverted (real) or upright (virtual) The image produced by a diverging lens is always virtual This means the image will always be upright

Potential divider diagram and equation

The input voltage Vin is applied to the top and bottom of the series resistors The output voltage Vout is measured from the centre to the bottom of resistor R2 The potential difference V across each resistor depends upon its resistance R: The resistor with the largest resistance will have a greater potential difference than the other one from V = IR If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share In potential divider circuits, the p.d across a component is proportional to its resistance from V = IR

Absolute Temperature

The kelvin temperature scale begins at absolute zero0 K is equal to -273 °C An increase of 1 K is the same change as an increase of 1 °C It is not possible to have a temperature lower than 0 K This means a temperature in kelvin will never have a negative value To convert between temperatures θ in the Celsius scale, and T in the Kelvin scale, use the following conversion: θ / °C = T / K − 273 T / K = θ / °C + 273 Conversion chart relating the temperature on the Kelvin and Celsius scales

Conductors, Insulators & Electrons

The key difference between conductors and insulators is that: Conductors allow charge carriers to freely move Insulators do not allow charge carriers to move The reasons for this are to do with their internal structure

Measuring Energy Usage (Calculating with kWh)

The kilowatt hour can also be defined using an equation: Where E = energy (kWh) P = power (kW) t = time (h) This equation is unusual because S.I. unit are not used, both energy and power are × 103, and time is in hours, not seconds Since the usual unit of energy is joules (J), this is the 1 W in 1 sTherefore: Since 1 kW = 1000 W and 1 h = 3600 s To convert between Joules and kW h: kWh x (3.6 x 10 6) = 6 J divided (3.6 x 10 6) = kWh The kW h is a large unit of energy, and mostly used for energy in homes, businesses, factories and so on

Kinetic Energy

The kinetic energy, EK, of an object (also known as its kinetic store) is defined as: The energy an object has as a result of its mass and speed This means that any object in motion has energy in its kinetic energy store Kinetic energy can be calculated using the equation: EK = ½ × m × v2 Where: EK = kinetic energy in Joules (J) m = mass of the object in kilograms (kg) v = speed of the object in metres per second (m/s)

Conservation of Energy

The law of conservation of energy states that: Energy cannot be created or destroyed, it can only be transferred from one energy store to another This means the total amount of energy in a closed system remains constant Therefore, energy cannot be 'lost', but it can be transferred to the thermal energy store of the surroundings Energy can be dissipated to the surroundings by radiation (by heat, light or sound) This energy is often not useful energy, so it can be described as wasted energy

Investigating Reflection (Analysis of Results)

The law of reflection states: i = r Where: i = angle of incidence in degrees (°)r = angle of reflection in degrees (°) If the experiment was carried out correctly, the angles should be the same

Investigating the Field Around a Wire

The magnetic field patterns due to currents in straight wires and in solenoids can be investigated using: A thick wire A solenoid (a wire wrapped into a coil) - for example, a metal slinky Cell, ammeter, variable resistor and connecting wires Cardboard with holes (the holes must be large enough for the wire to fit through)Clamp stand Iron filings or a compass Spread the iron filings uniformly on the cardboard and place the magnetic needle on the board Tap the cardboard slightly and observe the orientation of iron filings When the current direction is reversed, the compasses point in the opposite direction showing that the direction of the field reverses when the current reverses

Factors Affecting EM Induction

The magnitude (size) of the induced EMF is determined by: The speed at which the wire, coil or magnet is moved The number of turns on the coils of wire The size of the coils The strength of the magnetic field The direction of the induced potential difference is determined by: The orientation of the poles of the magnet 1. The speed at which the wire, coil or magnet is moved: Increasing the speed will increase the rate at which the magnetic field lines are cut This will increase the induced potential difference 2. The number of turns on the coils in the wire: Increasing the number of turns on the coils in the wire will increase the potential difference induced This is because each coil will cut through the magnetic field lines and the total potential difference induced will be the result of all of the coils cutting the magnetic field lines 3. The size of the coils: Increasing the area of the coils will increase the potential difference induced This is because there will be more wire to cut through the magnetic field lines 4. The strength of the magnetic field: Increasing the strength of the magnetic field will increase the potential difference induced 5. The orientation of the poles of the magnet: Reversing the direction in which the wire, coil or magnet is moved

Simple Consequences of Energy Transfer Conduction

The main means of thermal energy transfer in solids When heated, atoms vibrate more, knocking into each other and transferring energy from atom to atom as a result Metals are excellent conductors; Non-metals are poor; Liquids and gases are very poor If a question mentions metals, the answer will probably have something to do with conduction Trapped air is a very good insulator of heat. Air is a gas and so is a poor conductor. Trapping it prevents it from circulating and forming a convection current Thermal energy is transferred from the hot coffee to the mug and to the cold hands The mechanism by which the thermal energy is transferred is by either conduction, convection or radiation In this case the diagram focuses on conduction

Convection

The means of thermal energy transfer in liquids and gases When heated, a gas will expand and become less dense. This causes it to rise (a convection current). Cooler (denser) gas falls, replacing the hot gas If a question refers to a liquid or gas (that isn't trapped) then convection currents will probably form Heat sources placed at the bottom of things will generally create convection currents. Likewise, cooling units placed high up will cool any rising air, causing it to sink again Thermal energy is transferred from the hot coffee to the air by convection currents rising from the surface The mechanism by which the thermal energy is transferred is by either conduction, convection or radiation In this case the diagram focuses on convection

Fixed Points of Water

The melting and boiling points of pure water are known as fixed points Ice melts at 0 °C Pure water boils at 100 °C These are the accepted values for pure water at atmospheric pressure Ice melts at 0 °C and water boils at 100 °C

Arrangement & Motion of Particles (Solid)

The molecules are very close together and arranged in a regular pattern The molecules vibrate about fixed positions

Arrangement & Motion of Particles (Gas)

The molecules are widely separated - about 10 times further apart in each direction The molecules move about randomly at high speeds

Intermolecular Forces and Motion of Particles (Solids)

The molecules in a solid are held in place by strong intermolecular forces They only vibrate in position The distance between them is fixed This gives the solid its rigid shape and fixed volume

Effect of Nuclear Size on Decay

The most stable nuclei have roughly the same number of protons to neutrons If there were too many protons, then the repulsive force caused by them all having the same positive charge which cause the nucleus to repel when it becomes very large Therefore, if a nucleus has an imbalance of protons or neutrons, it is more likely to decay into small nuclei until it gets to a stable nucleus with roughly the same number of each Therefore, Isotopes of an element may be radioactive due to: An excess of neutrons in the nucleus The nucleus being too heavy An example of these are the isotope of hydrogen-1

The DC Motor

The motor effect can be used to create a simple d.c electric motor The simple d.c. motor consists of a coil of wire (which is free to rotate) positioned in a uniform magnetic field: A simple d.c. electric motor This causes the coil to rotate since it experiences a turning effect The turning effect is increased by increasing: The number of turns on the coil The current The strength of the magnetic field

Proton Number, Z

The number of protons in an atom is called its proton number (it can also be called the atomic number)Elements in the periodic table are ordered by their atomic number Therefore, the number of protons determines which element an atom is The atomic number of a particular element is always the same For example: Hydrogen has an atomic number of 1. It always has just one proton Sodium has an atomic number of 11. It has 11 protons Uranium has an atomic number of 92. It has 92 protons The atomic number is also equal to the number of electrons in an atom This is because atoms have the same number of electrons and protons in order to have no overall charge

Transformer Calculations

The output potential difference (voltage) of a transformer depends on:The number of turns on the primary and secondary coilsThe input potential difference (voltage) It can be calculated using the equation: This equation can be written using symbols as follows: WhereVp = potential difference (voltage) across the primary coil in volts (V)Vs = potential difference (voltage) across the secondary coil in volts (V)np = number of turns on primary coilns = number of turns on secondary coil The equation above can be flipped upside down to give: V s = N s V p = N p The equations above show that: The ratio of the potential differences across the primary and secondary coils of a transformer is equal to the ratio of the number of turns on each coil

Condensation

The particle diagrams next to the graph show that as a gas condenses into a liquid The gas has already lost heat energy (cooled down) The particles lose kinetic energy and move more slowly They no longer have enough energy to overcome the intermolecular forces of attraction between molecules The particles get closer together They only have enough energy to flow over one another The gas has condensed into a liquid with no change of temperature

Solidification

The particle diagrams next to the graph show that as a liquid solidifies into a solid The liquid has already lost heat energy (cooled down) The particles lose kinetic energy and move more slowly They no longer have enough energy to overcome the intermolecular forces of attraction between molecules The particles get closer together They only have enough energy to vibrate about their fixed position The liquid has solidified into a solid with no change of temperature Heating/cooling curve of a substance showing the energy changes as temperature is increased/decreased

Light Speed

The planets and moons of the solar system are visible from Earth when they reflect light from the Sun The outer regions of the Solar System are around 5 × 1012 m from the Sun, which means even light takes some time to travel these distances The Sun is so far away from Earth that the light we see actually left the Sun eight minutes earlier the nearest star to us after the Sun is so far away that light from it takes four years to reach us The Milky Way galaxy contains billions of stars, huge distances away, with the light taking even longer to be seen from Earth The speed of light is a constant 3 × 108 m/sTherefore, using the equation: The time taken to travel a certain distance can be calculated by rearranging to:

Three-pin Plug & Earth Connection

The plug socket and inside of a three-pin plug showing the three wires and their connections. The live and neutral wires deliver the electricity to the device. The Earth wire is for safety In order to protect the user or the device, there are several safety features built into domestic appliances, including: Double insulation Earthing Fuses Circuit breakers

What is stability?

The position of the centre of gravity of an object affects its stability An object is stable when its centre of gravity lies above its base The wider base an object has, the lower its centre of gravity and it is more stable The narrower base an object has, the higher its centre of gravity and the object is more likely to topple over if pushed

Calculating Pressure in Liquids

The pressure is more accurately the difference in pressure at different depths h in a liquid, since the pressure changes with the depth The pressure due to a column of liquid can be calculated using the equation Δp = ρgΔh Where: Δp = change in pressure in pascals (Pa) Where 1 Pa = 1 N/m2 ρ = density of the liquid in kilograms per metre cubed (kg/m3) g = gravitational field strength on Earth in newtons per kilogram (N/kg) Δh = change in height of the column in metres (m) The force from the pressure is exerted evenly across the whole surface of an object in a liquid, and in all directions

Conservation of Momentum

The principle of conservation of momentum states that: In a closed system, the total momentum before an event is equal to the total momentum after the event A closed system means the energy within the system is constant and there is an absence of external forces (e.g. friction) In other words: The total momentum before a collision = The total momentum after a collision A system is a certain number of objects under consideration This can be just one object or multiple objects Since momentum is a vector quantity, a system of objects moving in opposite directions (e.g. towards each other) at the same speed will have an overall momentum of 0 since they will cancel out Momentum is always conserved over time

Principle of Moments

The principle of moments states that: If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot Remember that the moment = force × distance from a pivot The forces should be perpendicular to the distance from the pivot For example, on a horizontal beam, the forces which will cause a moment are those directed upwards or downwards

Investigate refraction (Safety Considerations)

The ray box light could cause burns if touched Run burns under cold running water for at least five minute Looking directly into the light may damage the eyes Avoid looking directly at the light Stand behind the ray box during the experiment Keep all liquids away from the electrical equipment and paper

Investigating Reflection (Safety Considerations)

The ray box light could cause burns if touched Run burns under cold running water for at least five minute Looking directly into the light may damage the eyes Avoid looking directly at the light Stand behind the ray box during the experiment Keep all liquids away from the electrical equipment and paper Take care using the mirror Damages on the mirror can affect the outcome of the reflection experiment

Refractive Index

The refractive index is a number which is related to the speed of light in the material (which is always less than the speed of light in a vacuum): REFRACTIVE INDEX, n = SPEED OF LIGHT IN VACUUM SPEED OF LIGHT IN MATERIAL The refractive index is a number that is always larger than 1 and is different for different materials Objects which are more optically dense have a higher refractive index, e.g. n is about 2.4 for diamond Objects which are less optically dense have a lower refractive index, e.g. n is about 1.5 for glass Since refractive index is a ratio, it has no units

Proportionality Relationships for Electrical Conductors

The relationship between resistance, length and cross-sectional area can be represented mathematically Resistance is directly proportional to length Resistance is inversely proportional to cross-sectional area (width, or thickness) The mathematical relationship between length and width of the wire and the resistance

Safe Storage

The risks associated with handling radioactive sources can be minimised by following a few simple procedures: Store the sources in lead-lined boxes and keep at a distance from people Minimise the amount of time you handle sources for and return them to their boxes as soon as you have finished using them During use, keep yourself (and other people) as far from the sources as feasible. When handling the sources do so at arm's length, using a pair of tongs Radioactivity warning sign When using tongs, gloves and safety specs are usually unnecessary when handling radioactive materials, unless there is a risk of the material leaking on to things

Using Distance-Time Graphs

The speed of a moving object can be calculated from the gradient of the line on a distance-time graph: The rise is the change in y (distance) values The run is the change in x (time) values

Speed

The speed of an object is the distance it travels per unit time Speed is a scalar quantity This is because it only contains a magnitude (without a direction) For objects that are moving with a constant speed, use the equation below to calculate the speed: Where: Speed is measured in meter's per second (m/s) Distance travelled is measured in meter's (m) Time taken is measured in seconds (s

Gravitational Field Strength

The strength of gravity on different planets after an object's weight on that planet Weight is defined as: The force acting on an object due to gravitational attraction Planets have strong gravitational fields Hence, they attract nearby masses with a strong gravitational force Because of weight: Objects stay firmly on the ground Objects will always fall to the ground Satellites are kept in orbit Objects are attracted towards the centre of the Earth due to its gravitational field strength Both the weight of any body and the value of the gravitational field strength g differs between the surface of the Earth and the surface of other bodies in space, including the Moon because of the planet or moon's mass The greater the mass of the planet then the greater its gravitational field strength A higher gravitational field strength means a larger attractive force towards the centre of that planet or moon g varies with the distance from a planet, but on the surface of the planet, it is roughly the same The strength of the field around the planet decreases as the distance from the planet increases However, the value of g on the surface varies dramatically for different planets and moons The gravitational field strength (g) on the Earth is approximately 10 N/kg The gravitational field strength on the surface of the Moon is less than on the Earth This means it would be easier to lift a mass on the surface of the Moon than on the Earth The gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) is more than on the Earth This means it would be harder to lift a mass on the gas giants than on the Earth Value for g on the different objects in the Solar System On such planets such as Jupiter, an object's mass remains the same at all points in space However, their weight will be a lot greater meaning for example, a human will be unable to fully stand up A person's weight on Jupiter would be so large a human would be unable to fully stand up

Factors Affecting Magnetic Field Strength

The strength of the magnetic field produced around a solenoid can be increased by: Increasing the size of the current which is flowing through the wire Increasing the number of coils Adding an iron core through the centre of the coils The strength of an electromagnet can be changed by: Increasing the current will increase the magnetic field produced around the electromagnet Decreasing the current will decrease the magnetic field produced around the electromagnet

Composition of the Nucleus

The structure of the atom is made up of a: Positively charged nucleus at the centre (made up protons and neutrons) Negatively charged electrons in orbit around the nucleus Protons and neutrons are found in the nucleus of an atom Protons have a positive charge, whilst neutrons have no charge This is why the nucleus is overall positive

Beta Particles

The symbol for beta is β- Beta particles are fast-moving electrons They are produced in nuclei when a neutron changes into a proton and an electron Beta particles have a charge of -1 This means they can be affected by an electric field

Analysis of Results

The thermal energy supplied to the block can be calculated using the equation: E = IVt Where: E = thermal energy, in joules (J) I = current, in amperes (A) V = potential difference, in volts (V) t = time, in seconds (s) The change in thermal energy is defined by the equation: ΔE = mcΔθ Where: ΔE = change in thermal energy, in joules (J) m = mass, in kilograms (kg) c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C) Δθ = change in temperature, in degrees Celsius (°C) Rearranging for the specific heat capacity, c: To calculate Δθ: Δθ = final temperature - initial temperature To calculate ΔE: ΔE = IVtf - IVti Where: I = average current, in amperes (A) V = average potential difference (V) tf = final time, in seconds (s) ti = initial time, in seconds (s) These values are then substituted into the specific heat capacity equation to calculate the specific heat capacity of the aluminium block

Uses & Consequences of Thermal Expansion

The thermal expansion of materials can have some useful applications, but also has some undesirable consequences The increase in temperature... Leads to an increase in kinetic energy, so that... Molecules and atoms move more quickly... And move apart This separation of the the molecules makes the substance bigger!

Nucleon Number, A

The total number of particles in the nucleus of an atom is called its nucleon number (or mass number) The mass number is the number of protons and neutrons in the atom The number of neutrons can be found by subtracting the atomic number from the mass number Number of Neutrons = Nucleon Number - Proton Number For example, if a sodium atom has a mass number of 23 and an atomic number of 11, then the number of neutrons would be 23 - 11 = 12

Accretion Model of the Solar System

There are 4 rocky and small planets: Mercury, Venus, Earth and Mars These are the nearest to the Sun There are 4 gaseous and large planets: Jupiter, Saturn, Uranus and Neptune There are the furthest from the sun The eight planets of our Solar System The differences in the types of planets are defined by the accretion model for Solar System formation The Sun was thought to have formed when gravitational attraction of pulled together clouds of hydrogen dust and gas (called nebulae) The Solar System then formed around 4.5 billion years ago The planets were formed from the remnants of the disc cloud of matter left over from the nebula that formed the Sun These interstellar clouds of gas and dust included many elements that were created during the final stages of a star's lifecycle (a previous supernova) Gravity collapsed the matter from the nebula in on itself causing it to spin around the Sun The gravitational attraction between all the small particles caused them to join together and grow in an accretion process A rotating accretion disc is formed when the planets emerged The accretion model of the creation of the Solar System As the Sun grew in size it became hotter Where the inner planets were forming near the Sun, the temperature was too high for molecules such as Hydrogen, Helium, water and Methane to exist in a solid state Therefore, the inner planets are made of materials with high melting temperatures such as metals (e.g. iron)Only 1% of the original nebula is composed of heavy elements, so the inner, rocky planets could not grow much and stayed as a small size, solid and rocky The cooler regions were further away from the Sun, and temperature was low enough for the light molecules to exist in a solid state The outer planets therefore could grow to a large size up and include even the lightest element, Hydrogen These planets are large, gaseous and cold

Gravitational Attraction of the Sun

There are many orbiting objects in our solar system and they each orbit a different type of planetary body A smaller body or object will orbit a larger body For example, a planet orbiting the Sun In order to orbit a body such as a star or a planet, there has to be a force pulling the object towards that body Gravity provides this force Therefore, it is said that the force that keeps a planet in orbit around the Sun is the gravitational attraction of the Sun The gravitational force exerted by the larger body on the orbiting object is always attractive Therefore, the gravitational force always acts towards the centre of the larger body Therefore, the force that keeps an object in orbit around the Sun is the gravitational attraction of the Sun and is always directed from the orbiting object to the centre of the Sun The gravitational force will cause the body to move and maintain in a circular path Gravitational attraction causes the Moon to orbit around the Earth

Digital & Analogue Signals

There are two types of signals: Analogue Digital Analogue signals vary continuously - they can take any value An analogue signal is continuously varying, taking any value A digital signal can only take one of two (discrete) states These are usually referred to as;1s and 0sHighs and lows, or Ons and offs A digital signal can only take one of two values - 0 or 1

Nuclear Fission

There is a lot of energy stored within the nucleus of an atom This energy can be released in a nuclear reaction such as fission Nuclear fission is defined as: The splitting of a large, unstable nucleus into two smaller nuclei Isotopes of uranium and plutonium both undergo fission and are used as fuels in nuclear power stations During fission, when a neutron collides with an unstable nucleus, the nucleus splits into two smaller nuclei (called daughter nuclei) as well as two or three neutrons Gamma rays are also emitted Large nuclei can decay by fission to produce smaller nuclei and neutrons with a lot of kinetic energy The products of fission move away very quickly Energy transferred is from nuclear potential energy to kinetic energy The mass of the products (daughter nuclei and neutrons) is less than the mass of the original nucleus This is because the remaining mass has been converted into energy which is released during the fission process The processes involved in nuclear fission can be shown in different ways as diagrams These diagrams show how the reaction happens in a way that is easy to understand A neutron is fired into the target nucleus, causing it to split The diagram above is useful because it shows clearly the different parts of the fission reaction An example of a nuclide equation for fission is: energy Where: is an unstable isotope of Uranium is a neutron us an unstable isotope of Krypton is an unstable isotope of Barium The above equation represents a fission reaction in which a Uranium nucleus is hit with a neutron and splits into two smaller nuclei - a Krypton nucleus and a Barium nucleus, releasing three neutrons in the process The sum of top (nucleon) numbers on the left-hand side equals the sum of top number on the right-hand side: 235 + 1 = 92 + 141 + (3 × 1) The same is true for the lower (proton) numbers: 92 + 0 = 36 + 56 + (2 × 0)

Temperature, Surface Area & Air Movements

These factors all affect the rate of evaporation Increased temperature increases the kinetic energy of the molecules in the liquid Molecules with more energy are more likely to overcome the intermolecular forces holding them in the liquid state and escape the surface Therefore higher temperature leads to a higher rate of evaporation Molecules only escape the intermolecular forces of attraction at the surface of the liquid Therefore a larger surface area leads to a higher rate of evaporation Air movement carries away the water vapour which has just evaporatedThis dries the air and allows more water molecules to escape Therefore increasing air movement (when indoors this is sometimes called draughts) increases the rate of evaporation

Radio Waves & Microwaves

These two parts of the spectrum share a lot of similarities and applications Their main uses concern wireless communication - in fact, many things that people often assume use radio waves actually use microwaves (e.g. WiFi, radar, mobile phones, satellite communications) At very high intensities microwaves can also be used to heat things This is what happens in a microwave oven

Comparing Conduction in Tiles and Textiles

This demonstration shows why homes use rugs and carpets Find a tiled or stone area of floor In the same room leave a rug or bath towel (not a thin cloth, it must be thick) The textile must stay in place on the floor for several hours to ensure they are at thermal equilibrium (the same temperature) Stand with bare feet (hands can be used)Place one foot on the tiles or stone area, and the other on the textile (towel or rug)Observe the apparent temperature of the two materials as felt through the feet It will feel as though the tiles are cold while the rug is warm, however, they are at exactly the same temperature Explanation Tiles and stone are good conductors of heatWhere the foot touches the tiles, heat is transferred away from the foot, making it feel cold The foot has become colder since it lost heat to the tiles Textiles such as rugs are good insulators, meaning they are poor conductors of heat Where the foot touches the rug, heat is not transferred away from the foot This foot feels relatively warmer than the one which has lost heat to the tiles The foot has stayed at its starting temperature

Half-Life Graphs

To calculate the half-life of a sample from a graph: Check the original activity (where the line crosses the y-axies), A0Halve this value and look for this activity Go across from the halved value (on the y-axis) to the best fit curve, and then straight down to the x-axis The point where you reach the x-axis should be the half-life The time taken for the activity to decrease to half its original value is the half-life

Investigating Reflection (Aims of the Experiment)

To investigate reflection by a plane mirror Variables Independent variable = angle of incidence, i Dependent variable = angle of reflection, r Control variables: Distance of ray box from mirror Width of the light beam Same frequency / wavelength of the light Method Apparatus to investigate reflection Plain mirror Ray Box Line drawn 90° to mirror Protractor Set up the apparatus as shown in the diagram In the middle of the paper use a ruler to mark a straight line of about 10 cm long Use a protractor to draw a 90° line that bisects (cuts in half) the 10 cm line Place the mirror on the first line as shown in the diagram above Switch on the ray box and aim a beam of light at the point where the two drawn lines cross at an angle Use the pencil to mark two positions of the light beam: A point just after leaving the ray box The point on the reflected beam about 10 cm away from the mirror Remove the ray box and mirror Use a ruler to join the two marked positions to the point where the originally drawn lines crossed Use the protractor to measure the two angles from the 90° line. The angle for the ray towards the mirror is the angle of incidence, and the other is the angle of reflection Repeat the experiment three times with the beam of light aimed at different angles

Transverse Waves

Transverse waves are defined as: Waves where the points along its length vibrate at 90 degrees to the direction of energy transfer For a transverse wave: The energy transfer is in the same direction as the wave motion They transfer energy, but not the particles of the medium Transverse waves can move in a liquid or solid, but not a gas Some transverse waves (electromagnetic waves) can move in a vacuum The point on the wave that is: The highest above the rest position is called the peak, or crest The lowest below the rest position is called the trough Transverse waves can be seen in a rope when it is moved quickly up and down Examples of transverse waves are: Ripples on the surface of water Vibrations in a guitar string S-waves (a type of seismic wave)Electromagnetic waves (such as radio, light, X-rays etc)

Comparing Transverse & Longitudinal Waves (Property- Structure)

Transverse waves- Peaks and Troughs Longitudinal waves-compressions and rarefactions

Comparing Transverse & Longitudinal Waves (Property- Material)

Transverse waves- can move in liquids and solids, but not gases Longitudinal waves-can move in a gas, liquids and solids

Comparing Transverse & Longitudinal Waves (Property- Speed waves)

Transverse waves- defendant on material it is travelling in Longitudinal waves- dependant on materials it is travelling in

What are unbalanced forces?

Unbalanced forces mean that the forces have combined in such a way that they do not cancel out completely and there is a resultant force on the object For example, imagine two people playing a game of tug-of-war, working against each other on opposite sides of the rope If person A pulls with 80 N to the left and person B pulls with 100 N to the right, these forces do not cancel each other out completely Since person B pulled with more force than person A the forces will be unbalanced and the rope will experience a resultant force of 20 N to the right

Floating Objects (Upthrust)

Upthrust is a force that pushes upwards on an object submerged in a fluid i.e. liquids and gases It is always in the opposite direction to the object's weight This is why boats, and objects that are less dense than water, float The size of the upthrust depends on the density of the fluid as well as the volume of fluid that is displaced (which is equal to the volume of the object) The denser the liquid, the greater the upthrust it will exert on an object

How to set up equilibrium experiment

Use a meter ruler for the beam Suspend it via two Newton meters, one on each side, that each hang from a clamp stand F1 is the reading given on the left side Newton meter and F4 is the reading given on the right Create a loop of string, tie a tight knot and slide the ruler through it F3 will be the weight of a mass hook with 10 N weights suspended from this string F2 is the weight of the beam

Applications of EM Waves Table (Microwave)

Use- heating food communication (WiFi, mobile phone, satellites)

Applications of EM Waves Table (Infrared)

Use- remote controls fiber optic communication thermal imaging night vision heating or cooking things motion sensors electrical heaters infrared cameras

Galaxies & Redshift

Usually, when an object emits waves, the wavefronts spread out symmetrically If the wave source moves, the waves can become squashed together or stretched out Diagram showing the wavefronts produced from a stationary object and a moving object A moving object will cause the wavelength, λ, (and frequency) of the waves to change: The wavelength of the waves in front of the source decreases and the frequency increases The wavelength behind the source increases and the frequency decreases This effect is known as the Doppler effect The Doppler effect also affects light If an object moves away from an observer the wavelength of light increases This is known as redshift as the light moves towards the red end of the spectrum Redshift is: An increase in the observed wavelength of electromagnet radiation emitted from receding stars and galaxies Light from a star that is moving towards an observer will be blueshifted and light from a star moving away from an observer will be redshifted The observer behind observes a red shift The Milky Way is just one of billions of galaxies that make up the Universe Light emitted from distant galaxies appears redshifted when compared with light emitted on Earth The diagram below shows the light coming to us from a close object, such as the Sun, and the light coming to us from a distant galaxy Comparing the light spectrum produced from the Sun and a distant galaxy The diagram also shows that the light coming to us from distant galaxies is redshifted The lines on the spectrum are shifted towards the red end This indicates that the galaxies are moving away from us If the galaxies are moving away from us it means that the universe is expanding The observation of redshift from distant galaxies supports the Big Bang theory Another observation from looking at the light spectrums produced from distant galaxies is that the greater the distance to the galaxy, the greater the redshift This means that the further away a galaxy, the faster it is moving away from us Graph showing the greater the distance to a galaxy, the greater the redshift

The Visible Spectrum of Light

Visible light is defined as the range of wavelengths which are visible to humans Visible light is the only part of the spectrum detectable by the human eye However, it only takes up 0.0035% of the whole electromagnetic spectrum In the natural world, many animals, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light The different colours of waves correspond to different wavelengths: Red has the longest wavelength (and the lowest frequency and energy) Violet has the shortest wavelength (and the highest frequency and energy) The colours of the visible spectrum: red has the longest wavelength; violet has the shortest

Wavelength

Wavelength is defined as: The distance from one point on the wave to the same point on the next wave In a transverse wave: The wavelength can be measured from one peak to the next peak In a longitudinal wave The wavelength can be measured from the centre of one compression to the centre of the next The wavelength is given the symbol λ (lambda) and is measured in metres (m) The distance along a wave is typically put on the x-axis of a wave diagram

Transverse Waves

Waves are repeated vibrations that transfer energy Energy is transferred by parts of the wave knocking nearby parts This is similar to the effect of people knocking into one another in a crowd, or a "Mexican Wave" at football matches Waves can exist as one of two types: Transverse Longitudinal

Waves - Basic

Waves transfer energy and information Waves are described as oscillations or vibrations about a fixed point For example, ripples cause particles of water to oscillate up and down Sound waves cause particles of air to vibrate back and forth In all cases, waves transfer energy without transferring matter For water waves, this means it is the wave and not the water (the matter) itself that travels For sound waves, this means it is the wave and not the air molecules (the matter) itself that travels Objects floating on water provide evidence that waves only transfer energy and not matter

Different properties of Nuclear Radiation (Alpha α)

What is it- 2 protons +2 neutrons Charge- +2 Range in air- few cm Penetration- stopped by paper Ionisation- high

Different properties of Nuclear Radiation (Beta β)

What is it- Electron Charge- -1 Range in air- few 10s of cm Penetration- stopped by few mm Aluminium Ionisation- medium

Different properties of Nuclear Radiation (Gamma γ)

What is it- electromagnetic wave Charge- 0 Range in air- infinite Penetration- reduced by few mm lead Ionisation- low

Experiment 1: Moving a magnet through a coil

When a coil is connected to a sensitive voltmeter, a bar magnet can be moved in and out of the coil to induce an EMF A bar magnet is moved through a coil connected to a voltmeter to induce an EMF The expected results are: When the bar magnet is not moving, the voltmeter shows a zero reading When the bar magnet is held still inside, or outside, the coil, there is no cutting of magnetic field lines, so, there is no EMF induced When the bar magnet begins to move inside the coil, there is a reading on the voltmeter As the bar magnet moves, its magnetic field lines 'cut through' the coil This induces an EMF within the coil, shown momentarily by the reading on the voltmeter When the bar magnet is taken back out of the coil, an e.m.f is induced in the opposite direction (a result of Lenz's law)As the magnet changes direction, the direction of the current changes The voltmeter will momentarily show a reading with the opposite sign Increasing the speed of the magnet induces an e.m.f with a higher magnitude The direction of the electric current, and e.m.f, induced in the conductor is such that it opposes the change that produces it This is Lenz's law An e.m.f is induced only when the bar magnet is moving through the coil Factors that will increase the induced EMF are: Moving the magnet faster through the coil Adding more turns to the coil Increasing the strength of the bar magnet

Magnetic Field Around Wires & Solenoids

When a current flows through a conducting wire a magnetic field is produced around the wire A conducting wire is any wire that has current flowing through it The shape and direction of the magnetic field can be investigated using plotting compasses The compasses would produce a magnetic field lines pattern that would like look the following Diagram showing the magnetic field around a current-carrying wire The magnetic field is made up of concentric circles A circular field pattern indicates that the magnetic field around a current-carrying wire has no poles As the distance from the wire increases the circles get further apart This shows that the magnetic field is strongest closest to the wire and gets weaker as the distance from the wire increases The right-hand thumb rule can be used to work out the direction of the magnetic field The right-hand thumb rule shows the direction of current flow through a wire and the direction of the magnetic field around the wire Reversing the direction in which the current flows through the wire will reverse the direction of the magnetic field Side and top view of the current flowing through a wire and the magnetic field produced If there is no current flowing through the conductor there will be no magnetic field Increasing the amount of current flowing through the wire will increase the strength of the magnetic field This means the field lines will become closer together

Calculating Power Losses

When a current passes through a wire, the current creates a heating effect which means the wires warm up This means they lose electrical energy as heat which reduced the efficiency of the transformer This is due to electrical resistance which is present in all wires The power (energy per second) lost in the wire is given by the following equation P = I2R Where: P = power in watts (W) I = current in amps (A) R = resistance in ohms (Ω) Since the power is the energy lost per second, the total energy lost in a time t will be: E = P × t Where: E = energy in joules (J) t = time in seconds (s) A step-up transformer may be used to increase the voltage of a power supply from the power station to the transmission wires The number of turns and voltage for the transformer is related by the following equation: Where: Vp = potential difference (voltage) across the primary coil in volts (V) Vs = potential difference (voltage) across the secondary coil in volts (V) np = number of turns on the primary coil ns = number of turns on the secondary coil A step-up transformer has more turns on the secondary coil, Ns, than on the primary coil, Np Since a transformer cannot output more power than is put into it, increasing the voltage must result in the current being lowered IpVp = IsVs Where: Ip = current in the primary coil in amps (A) Is = current in the secondary coil in amps (A) Lower current results in less power and energy loss in the cables This makes the transfer of electrical energy through the wires more efficient

Charged Particles in a Magnetic Field

When a current-carrying wire is placed in a magnetic field, it will experience a force if the wire is perpendicular This is because the magnetic field exerts a force on each individual electron flowing through the wire Therefore, when a charged particle passes through a magnetic field, the field can exert a force on the particle, causing it to deflect The force is always at 90 degrees to both the direction of travel and the magnetic field lines The direction can be worked out by using Fleming's left-hand rule In the case of a electron in a magnetic field the second finger points in the opposite direction to the direction of motion Conventional current is said to flow opposite to the direction of flow of electrons The finger represents current An alternative is to use the right hand to work out directions for charged particles When a charged particle (such as an electron) enters a magnetic field, it is deflected by the field If the particle is travelling perpendicular to the field lines: It will experience the maximum force If the particle is travelling parallel to the field lines: It will experience no force If the particle is travelling at an angle to the field lines:It will experience a small force

Experiment 2: Moving a wire through a magnet

When a long wire is connected to a voltmeter and moved between two magnets, an EMF is induced The pattern of a magnetic field in a wire can be investigated using this set up Note: there is no current flowing through the wire to start with A wire is moved between two magnets connected to a voltmeter to induce an EMF The expected results are: When the wire is not moving, the voltmeter shows a zero reading When the wire is held still inside, or outside, the magnets, the rate of change of flux is zero, so, there is no EMF induced As the wire is moved through between the magnets, an EMF is induced within the wire, shown momentarily by the reading on the voltmeter As the wire moves, it 'cuts through' the magnetic field lines of the magnet, generating a change in magnetic flux When the wire is taken back out of the magnet, an EMF is induced in the opposite direction As the wire changes direction, the direction of the current changes The voltmeter will momentarily show a reading with the opposite sign As before, the direction of the electric current, and e.m.f, induced in the conductor is such that it opposes the change that produces it Factors that will increase the induced e.m.f are: Increasing the length of the wire Moving the wire between the magnets faster Increasing the strength of the magnets

Temporary (Induced) Magnets

When a magnetic material is placed in a magnetic field, the material can temporarily be turned into a magnet This is called induced magnetism Some objects such as paperclips or needles (which are made from steel) can be magnetised and will remain magnetic for a while Other objects, such as electromagnets or transformers (which are made from iron) will be demagnetised as soon as the cause of the induced magnetism is removed When magnetism is induced on a material: One end of the material will become a north pole The other end will become a south pole Magnetic materials will always be attracted to a permanent magnet This means that the end of the material closest to the magnet will have the opposite pole to magnets pole closest to the material Inducing magnetism in a magnetic material When the magnetic material is removed from the magnetic field it will lose most/all of its magnetism quickly

Impulse

When a resultant (unbalanced) force acts on a mass, the momentum of that mass will change The impulse of a force is equal to that force multiplied by the time for which it acts: impulse = force × change in time impulse = FΔt The change in momentum of a mass is equal to the impulse provided by the force: impulse = change in momentum impulse = FΔt = Δp Change in momentum can also be described as: Δp = Δ(mv) Δp = mv − mu Where: m = mass in kg v = final velocity in m/s u = initial velocity in m/s Therefore: impulse = FΔt = Δp = mv − mu

Magnetic Field Around a Solenoid

When a wire is looped into a coil, the magnetic field lines circle around each part of the coil, passing through the centre of it Diagram showing the magnetic field around a flat circular coil To increase the strength of the magnetic field around the wire it should be coiled to form a solenoid The magnetic field around the solenoid is similar to that of a bar magnet Magnetic field around and through a solenoid The magnetic field inside the solenoid is strong and uniform One end of the solenoid behaves like the north pole of a magnet; the other side behaves like the south pole To work out the polarity of each end of the solenoid it needs to be viewed from the end If the current is travelling around in a clockwise direction then it is the south pole If the current is travelling around in an anticlockwise direction then it is the north pole If the current changes direction then the north and south poles will be reversed If there is no current flowing through the wire then there will be no magnetic field produced around or through the solenoid Poles of a Solenoid

Reflection in a Plane Mirror

When an object is placed in front of a mirror, an image of that object can be seen in the mirror The image will be: The same size as the object The same distance behind the mirror as the object is in front of it Directly in line with the object The formation of this image can be understood by drawing a ray diagram Diagram showing the formation of an image in a mirror by the reflection of light Light from the object hits the mirror, reflecting from it (i=r) To an observer, the reflected ray appears to have come from the right-hand side of the mirror The reflected ray can be traced back in this directions, forming a virtual ray This can be repeated for another ray travelling in a slightly different direction An image of the object will appear where these two virtual rays cross The type of image formed in the mirror is called a virtual image A virtual image is formed by the divergence of rays from the image, and cannot be projected onto a piece of paper (because the rays don't actually go through the image)

Investigating the Centre of Gravity

When an object is suspended from a point, the object will always settle so that its centre of gravity comes to rest below the pivoting point This can be used to find the centre of gravity of an irregular shape

Types of Radioactive Decay

When an unstable nucleus decays, it emits radiation called nuclear radiation There are different types of radiation that can be emitted: Alpha (α) particles Beta (β-) particles Gamma (γ) radiation These changes are spontaneous and random

Features of a Wave

When describing wave motion, there are several terms which are important to know, including: Crest(Peak) Trough Amplitude Wavelength Frequency Wavespeed Wavefront

Ray Diagrams for Refraction

When drawing refraction ray diagrams, angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary The angle of the wave approaching the boundary is called the angle of incidence (i) The angle of the wave leaving the boundary is called the angle of refraction (r) The line at right angles (90°) to the boundary is known as the normal When drawing a ray diagram an arrow is used to show the direction the wave is travelling An incident ray has an arrow pointing towards the boundary A refracted ray has an arrow pointing away from the boundary The angles of incidence and refraction are usually labelled i and r respectively A ray diagram for light refracting at a boundary, showing the normal, angle of incidence and angle of refraction

Advantages of High Voltage Transmission

When electricity is transmitted over large distances, the current in the wires heats them, resulting in energy loss To transmit the same amount of power as the input power the potential difference at which the electricity is transmitted should be increased This will result in a smaller current being transmitted through the power lines This is because P = IV, so if V increases, I must decrease to transmit the same power A smaller current flowing through the power lines results in less heat being produced in the wire This will reduce the energy loss in the power lines Electricity is transmitted at high voltage, reducing the current and hence power loss in the cables

Snell's Law

When light enters a denser medium (such as glass) it slows down and bends towards the normal How much the light bends depends on the density of the material Angle of incidence i and angle of refraction r through a glass block If light travels from a less dense to a more dense medium (e.g. air to glass), r < i (bends towards the normal) If light travels from a more dense to a less dense medium (e.g. glass to air), r > i (bends away from the normal) The angles of incidence and refraction are related by an equation known as Snell's Law: n = sin i sin r Where: n = the refractive index of the material i = angle of incidence of the light (°) r = angle of refraction of the light (°) 'Sin' is the trigonometric function 'sine' which is on a scientific calculator

Boiling

When liquid water is heated by adding thermal energy (say from the gas flame or kettle element), the temperature of the water rises until the water boils At the boiling point, even if more thermal energy is added, the liquid water does not get any hotter This means that the internal energy is not rising The additional thermal energy goes into overcoming the intermolecular forces between the molecules of wate rAs the forces are overcome, the liquid water becomes water vapour (steam)This is evaporation or vaporisation; the water is now a gas The process is repeated backwards for cooling as energy is transferred away A gas turns back into liquid through condensation

Thermal Expansion

When materials are heated, they expand This expansion happens because the molecules start to move around (or vibrate) faster, which causes them to knock into each other and push each other apart When a solid is heated, the molecules vibrate more, pushing each other apart Note: When this happens, it is the space taken up by the molecules that increases. The molecules themselves remain the same size. Thermal expansion occurs in solids, liquids and gases When temperature is increased (at constant pressure); Solids will tend to expand the least Gases expand the most Liquids fall in between the two

Right-Hand Dynamo Rule

When moving a wire through a magnetic field, the direction of the induced EMF can be worked out by using the Right-Hand Dynamo rule The Right-Hand Dynamo rule can be used to deduce the direction of the induced EMF To use the rule: First Finger = Field: Start by pointing the first finger (on the right hand) in the direction of the field ThuMb = Motion: Next, point the thumb in the direction that the wire is moving in SeCond = Current: The Second finger will now be pointing in the direction of the current (or, strictly speaking, the EMF) The direction of the induced EMF always opposes the change that produces itThis means that any magnetic field created by the EMF will act so that it tries to stop the wire or magnet from moving

Orbital Speed

When planets move around the Sun, or a moon moves around a planet, they orbit in circular motion This means that in one orbit, a planet travels a distance equal to the circumference of a circle (the shape of the orbit) This is equal to 2πr where r is the radius a circle The relationship between speed, distance and time is: the average orbital speed of an object can be defined by the equation: Where: v = orbital speed in metres per second (m/s) r = average radius of the orbit in metres (m) T = orbital period in seconds (s) This orbital period (or time period) is defined as: The time taken for an object to complete one orbit The orbital radius r is always taken from the centre of the object being orbited to the object orbiting Orbital radius and orbital speed of a planet moving around a Sun

Resistors in Parallel

When resistors are connected in parallel, the combined resistance decreases and is less than the resistance of any of the individual components If two resistors of equal resistance are connected in parallel, then the combined resistance will halve The above resistors will have a combined resistance of 2 Ω − half the value of each resistor

Melting

When solid water (ice) is heated by adding thermal energy (from the surroundings, or a flame), the ice melts At the melting point, even if more thermal energy is added, the solid water does not get warmer This means that the internal energy is not rising The additional thermal energy goes into overcoming the intermolecular forces between the molecules of the solid ice As the forces are overcome, the solid water becomes liquid This is melting; the ice is now a liquid The process is repeated backwards for cooling as heat is transferred away A liquid turns back into a solid through freezing

Operation of a DC Motor

When the current is flowing in the coil at 90o to the direction of the magnetic field: The current creates a magnetic field around the coil The magnetic field produced around the coil interacts with the field produced by the magnets This results in a force being exerted on the coil The direction of the force can be determined using Fleming's left-hand rule As current will flow in opposite directions on each side of the coil, the force produced from the magnetic field will push one side of the coil up and the other side of the coil down This will cause the coil to rotate, and it will continue to rotate until it is in the vertical position In the vertical position momentum keeps the coil turning until the magnetic force takes over again The split ring commutator swaps the contacts of the coil This reverses the direction in which the current is flowing every half turn This keeps the current leaving the motor in the same direction (d.c) Reversing the direction of the current will also reverse the direction in which the forces are acting As a result, the coil will continue to rotate Forces on coil after commutator has reversed the direction of the current The split-ring commutator reverses the direction of the current in the coil every half turn This will keep the coil rotating continuously as long as the current is flowing

Direct & Alternating Current

When two oppositely charged conductors are connected together (by a length of wire), charge will flow between the two conductors Charge can flow between two conductors This flow of charge is called an electric current The greater the flow of charge, the greater the electric current

Resistors in Series

When two or more components are connected in series: The combined resistance of the components is equal to the sum of individual resistances When several components are connected in series, their combined resistance is equal to the sum of their individual resistances

Variable Potential Dividers

When two resistors are connected in series, the potential difference across the power source is shared between them A potential divider splits the potential difference of a power source between two components The potential difference across each resistor depends upon its resistance: The resistor with the largest resistance will have a greater potential difference than the other one If the resistance of one of the resistors is increased, it will get a greater share of the potential difference, whilst the other resistor will get a smaller share A potentiometer is a single component that (in its simplest form) consists of a coil of wire with a sliding contact, midway along it A potentiometer is a kind of variable resistor The sliding contact has the effect of separating the potentiometer into two parts - an upper part and a lower part - both of which have different resistances Moving the slider (the arrow in the diagram) changes the resistances (and hence potential differences) of the upper and lower parts of the potentiometer If the slider in the above diagram is moved upwards, the resistance of the lower part will increase and so the potential difference across it will also increase

Resistors as Potential Dividers

When two resistors are connected in series, through Kirchhoff's Second Law, the potential difference across the power source is divided between them Potential dividers are circuits which produce an output voltage as a fraction of its input voltage Potential dividers have two main purposes: To provide a variable potential difference To enable a specific potential difference to be chosen To split the potential difference of a power source between two or more components Potential dividers are used widely in volume controls and sensory circuits using LDRs and thermistors Potential divider circuits are based on the ratio of voltage between components. This is equal to the ratio of the resistances of the resistors in the diagram below, giving the following equation:

Uses of Ultrasound

When ultrasound reaches a boundary between two media, some of the waves are partially reflected The remainder of the waves continue through the material and are transmitted Ultrasound transducers are able to: Emit ultrasound Receive ultrasound The time taken for the reflections to reach a detector can be used to determine how far away a boundary is This is because ultrasound travels at different speeds through different media This is by using the speed, distance, time equation Where: v = speed in metres per second (m/s) s = distance in metres (m) t = time in seconds (s) This allows ultrasound waves to be used for both medical and industrial imaging

Dispersion of Light

White light is a mixture of all the colours of the spectrum Each colour has a different wavelength (and frequency), making up a very narrow part of the electromagnetic spectrum White light may be separated into all its colours by passing it through a prism This is done by refraction Violet light is refracted the most, whilst red light is refracted the least This splits up the colours to form a spectrum This process is similar to how a rainbow is created White light may be separated into all its colours by passing it through a prism

Work Done & Energy Transfers

Work is done when an object is moved over a distance by a force applied in the direction of its displacement It is said that the force does work on the object If a force is applied to an object but doesn't result in any movement, no work is done Work is done when a force is used to move an object The formula for work done is: Work done = force × distance W = fd

Experiment to find the centre of gravity of an irregular shape

1- The irregular shape (a plane laminar) is suspended from a pivot and allowed to settle 2- A plumb line (lead weight) is then held next to the pivot and a pencil is used to draw a vertical line from the pivot (the centre of gravity must be somewhere on this line) 3- The process is then repeated, suspending the shape from two different points The centre of gravity is located at the point where all three lines cross

Life Cycle of Stars

1. Nebula All stars form from a giant interstellar cloud of hydrogen gas and dust called a nebula 2. Protostar The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar As the particles are pulled closer together the density of the protostar will increase This will result in more frequent collisions between the particles which causes the temperature to increase 3. Main Sequence Star Once the protostar becomes hot enough, nuclear fusion reactions occur within its core The hydrogen nuclei will fuse to form helium nuclei Every fusion reaction releases heat (and light) energy which keeps the core hot Once a protostar is formed, its life cycle will depend on its mass The different life cycles are shown below: Flow diagram showing the life cycle of a star which is the same size as the Sun (solar mass) and the lifecycle of a star which is much bigger than the Sun Once a star is born it is known as a main-sequence star During the main sequence, the star is in equilibrium and said to be stable The inward force due to gravity is equal to the outward pressure force from the fusion reactions 4. Red Giant or Red Super Giant After several billion years the hydrogen causing the fusion reactions in the star will begin to run out Once this happens, the fusion reactions in the core will start to die down This causes the core to shrink and heat up The core will shrink because the inward force due to gravity will become greater than the outward force due to the pressure of the expanding gases as the fusion dies down A new series of reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium These reactions will cause the outer part of the star to expand A star the same size as the Sun or smaller will become a red giant A star much larger than the Sun will become a red super giant It is red because the outer surface starts to cool 5. For Red Giant Stars Planetary Nebula Once this second stage of fusion reactions have finished, the star will become unstable and eject the outer layer of dust and gas The layer of dust and gas which is ejected is called a planetary nebula 6. For Red Super Giants Supernova Once the fusion reactions inside the red supergiant finally finish, the core of the star will collapse suddenly causing a gigantic explosionThis is called a supernova At the centre of this explosion a dense body, called a neutron star will form The outer remnants of the star will be ejected into space during the supernova explosion, forming a planetary nebulaThe nebula from a supernova may form new stars with orbiting planets Neutron Star (or Black Hole) In the case of the biggest stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole A black hole is an extremely dense point in space that not even light can escape from Lifecycle of a star much larger than our Sun

Experiment 3: Measuring Density of Liquids

1.Place an empty measuring cylinder on a digital balance and note down the mass 2.Fill the cylinder with the liquid and note down the volume 3.Note down the new reading on the digital balance 4.Repeat these measurements and take an average before calculating the density Analysis of Results Find the mass of the liquid by subtracting the final reading from the original reading Mass of liquid = Mass of cylinder with water - mass of cylinder Remember to convert between grams (g) and kilograms (kg) by dividing by 1000 1 g = 0.001 kg 78 g = 0.078 kg Once the mass and volume of the liquid are known, the density can be calculated using the equation: Evaluating the Experiments Systematic Errors: Ensure the digital balance is set to zero before taking measurements of mass This includes when measuring the density of the liquid - remove the measuring cylinder and zero the balance before adding the liquid Random Errors: A main cause of error in this experiment is in the measurements of length Ensure to take repeat readings and calculate an average to keep this error to a minimum Place the irregular object in the displacement can carefully, as dropping it from a height might cause water to splash which will lead to an incorrect volume reading

Power rating (A star like the sun)

100 000 000 000 000 000 000MW

Power rating (A Saturn V space rocket)

100MW

Power rating (An electric light bulb)

100W

Method 2: Measuring the speed of sound using echoes

11)A person stands about 50 m away from a wall (or cliff) using a trundle wheel to measure this distance 2)The person claps two wooden blocks together and listens for the echo 3)A second person has a stopwatch and starts timing when they hear one of the claps and stops timing when they hear the echo 4)The process is then repeated 20 times and an average time calculated 5)The distance travelled by the sound between each clap and echo will be (2 × 50) m 6)The speed of sound can be calculated from this distance and the time using the equation: SPEED OF SOUND = 2 x DISTANCE TO THE WALL TIME TAKING

Approximate Density (kg/m3) of Lead

11300

Crests & Troughs

A crest, or a peak, is defined as: The highest point on a wave above the equilibrium, or rest, position A trough is defined as The lowest point on a wave below the equilibrium, or rest, position

Distance-Time Graphs

A distance-time graph shows how the distance of an object moving in a straight line (from a starting position) varies over time:

Fuses & Trip Switches

A fuse is a safety device designed to cut off the flow of electricity to an appliance if the current becomes too large (due to a fault or a surge) The circuit symbol for a fuse - take care not to confuse this with a resistor Fuses usually consist of a glass cylinder which contains a thin metal wire. If the current in the wire becomes too large:The wire heats up and meltsThis causes the wire to break, breaking the circuit and stopping the current A trip switch, found in the Consumer Box (where the electricity enters the building) does the same job as a fuseWhen the current is too high the switch 'trips' (automatically flicks to the off position)This stops current flowing in that circuit

Converging & Diverging Lenses

A lens is a piece of equipment that forms an image by refracting light There are two types of lens: Converging Diverging

Transformer

A transformer is an electrical device that can be used to increase or decrease the potential difference of an alternating current (voltage transformations) This is achieved using the generator effect A basic transformer consists of: A primary coil A secondary coil A soft iron core Iron is used because it is easily magnetised Structure of a transformer

Will a wooden block float and what is its density?

A wooden block will be partially submerged but will still float This is because the density of a wooden block (0.9 g/cm3) is slightly less than the density of water

Acceleration

Acceleration is defined as the rate of change of velocity In other words, it describes how much an object's velocity changes every second The equation below is used to calculate the average acceleration of an object: Where: a = acceleration in metres per second squared (m/s2)Δv = change in velocity in metres per second (m/s)Δt = time taken in seconds (s) The change in velocity is found by the difference between the initial and final velocity, as written below: change in velocity = final velocity − initial velocity Δv = v − u Where: v = final velocity in metres per second (m/s)u = initial velocity in metres per second (m/s) The equation for acceleration can be rearranged with the help of a formula triangle as shown

Thermal Radiation

All objects give off thermal radiation The hotter an object is, the more thermal radiation it emits Thermal radiation is the part of the electromagnetic spectrum called infrared Thermal radiation is the only way in which heat can travel through a vacuumIt is the way in which heat reaches us from the Sun through the vacuum of space The colour of an object affects how good it is at emitting and absorbing thermal radiation:

Alternative method

An electronic charge detector can be used in place of the Gold-leaf Electroscope

Will a iron block float and what is its density?

An iron block will sink This is because iron has a density (7.9 g/cm3) that is much higher than water

Bio Fuels

Biofuels are made from plant matter Energy from sunlight is transferred to the chemical store of plants Ethanol or methane can be produced and used in place of fossil fuels However, they have only half the energy density of fossil fuels

Orbiting Objects or Bodies in Our Solar System (comet)

Body or Object- comet What it Orbits- sun

Relative Thermal Conductivity

Conductors tend to be metals Better thermal conductors are those with delocalised electrons which can easily transfer energy This means that there is a wide range of thermal conductivity

Dangers of EM Waves (Radio)

Danger- not known danger

Examples of Scalar

Distance Speed Mass Energy Temperature Time

Applications of the Magnetic Effect

Electromagnets are used in a wide variety of applications, including: Relay circuits (utilised in electric bells, electronic locks, scrapyard cranes etc)Loudspeakers & headphones

Energy Transfers

Energy can be transferred between stores through different energy transfer pathways Examples of these are: Mechanical Electrical Heating Radiation

Example of pressure nails

Example 2: Nails Nails have sharp pointed ends with a very small area This concentrates the force, creating a large pressure over a small area This allows the nail to be hammered into a wall

Gamma Rays

Gamma rays are very dangerous and can be used to kill cells and living tissue This property can be utilised in both cancer detection and treatment If these gamma rays are carefully aimed at cancerous tissue, they can be very effective at destroying the cancerous cells Gamma rays can also be used to sterilise food and medical equipment by killing off the bacteria

Representing Lenses

In diagrams, the following symbols are often used to represent each type of lens: Concave and convex symbols

Electrical Conduction in Metals

In a metal, current is caused by a flow of electrons In metals, the current is caused by a flow of free (delocalised) electrons

Potential Difference in Series Circuits EXTENDED

In a series circuit, the sum of potential differences across the components is equal to the total EMF of the power supply In a series circuit the components share the EMF of the power supply

Applying Newton's First Law

Newton's first law is used to explain why things move with a constant (or uniform) velocity If the forces acting on an object are balanced, then the resultant force is zero The velocity (i.e. speed and direction) can only change if a resultant force acts on the object

What does Newton's first law of motion state?

Newton's first law of motion states: Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force This means if the resultant force acting on an object is zero: The object will remain stationary if it was stationary before The object will continue to move at the same velocity if it was moving When the resultant force is not zero The speed of the object can change The direction of the object can change

Pressure

Pressure is defined as The concentration of a force or the force per unit area For example, when a drawing pin is pushed downwards: It is pushed into the surface, rather than up towards the finger This is because the sharp point is more concentrated (a small area) creating a larger pressure

Demonstrating Wave Motion

Properties of waves, such as frequency, wavelength and wave speed, can be observed using water waves in a ripple tank Wave motion of water waves may be demonstrated using a ripple tank The wavelength of the waves can be determined by: Using a ruler to measure the length of the screen Dividing this distance by the number of wavefronts The frequency can be determined by: Timing how long it takes for a given number of waves to pass a particular point Dividing the number of wavefronts by the time taken The wave speed can then be determined by: Using the equation wave speed = frequency × wavelength

Equipment (Kettle)

Purpose- to boil water

Tissue Damage

Radiation is effectively used to destroy cancerous tumour cells However, it can cause damage to healthy tissue if it is not properly targeted This is mostly from high-energy radiation such as gamma rays and X-rays

Examples of vectors and scalars that are similar to each other

Scalar Vector Distance Displacement Speed Velocity Mass Weight

Scalars

Scalars are quantities that have only a magnitude For example, mass is a scalar since it is a quantity that has magnitude without a direction Distance is also a scalar since it only contains a magnitude, not a direction

Alpha Particles

The symbol for alpha is α An alpha particle is the same as a helium nucleus This is because they consist of two neutrons and two protons Alpha particles have a charge of +2 This means they can be affected by an electric field

Worked Example In the diagram above, a very high-frequency sound wave is used to check for internal cracks in a large steel bolt. The oscilloscope trace shows that the bolt does have an internal crack. Each division on the oscilloscope represents a time of 0.000002 s. The speed of sound through steel is 6000 m/s. Calculate the distance, in cm, from the head of the bolt to the internal crack.

Step 1: List the known quantities Speed of ultrasound, v = 6000 m/s Time taken, t = 5 × 0.000002 = 0.00001 s Step 2: Write down the equation relating speed, distance and time distance, d = v × t Step 3: Calculate the distance d = 6000 × 0.00001 = 0.06 m Step 4: Convert the distance to cm d = 6 cm

Multiple readings

Suppose you have to measure the thickness of a sheet of paper -The thing that you are trying to measure is so small that it would be very difficult to get an accurate answer If, however, you measure the thickness of 100 sheets of paper you can do so much more accurately -Dividing your answer by 100 will then give an accurate figure for the thickness of one sheet This process of taking a reading of a large number of values and then dividing by the number, is a good way of getting accurate values for small figures, including (for example) the time period of a pendulum -Measure the time taken for 10 swings and then divide that time by 10 to find the average

Investigate refraction (Evaluating the Experiment)

Systematic Errors: An error could occur if the 90° lines are drawn incorrectly Use a set square to draw perpendicular lines Random Errors: The points for the incoming and reflected beam may be inaccurately marked Use a sharpened pencil and mark in the middle of the beam The protractor resolution may make it difficult to read the angles accurately Use a protractor with a higher resolution

Electromotive Force

The Electromotive Force (e.m.f.) is the name given to the potential difference of the power source in a circuit It is defined as The electrical work done by a source in moving a unit charge around a complete circuit The Electromotive Force (EMF) is measured in volts (V) The EMF is the voltage supplied by a power supply: 12 V in the above case

Relative Charge

The different particles that make up atoms have different properties Relative mass is a way of comparing particles. It is measured in atomic mass units (amu) A relative mass of 1 is equal to mass of 1.67 × 10-27 kg Charge can be positive or negative Relative charge is, again, used to compare particles The fundamental charge is equal to the size of the charge on a proton and an electron, however the electron's charge is negative

The Greenhouse Effect

The rate of absorption and emission of radiation on Earth contributes to the Greenhouse Effect This is the natural process that warms the Earth's surface from the Sun The Sun's thermal radiation reaches the Earth's atmosphere where: Some radiation is reflected back to space Any radiation not reflected is absorbed and re-radiated by greenhouse gases The absorbed radiation then warms the atmosphere and the surface of the Earth This is similar to what happens in a greenhouse to keep a humid, and warm temperature to grow plants

What is equilibrium?

The term equilibrium means that an object keeps doing what it's doing, without any change Therefore: If the object is moving it will continue to move (in a straight line) If it is stationary it will remain stationary The object will also not start or stop turning The above conditions require two things: The forces on the object must be balanced There must be no resultant force The sum of clockwise moments on the object must equal the sum of anticlockwise moments there must be no resultant moment If the above two conditions are met, then the object will be in equilibrium

Safety Precautions

To mitigate the risks of radiation exposure, there are some safe practices that should be used: Radioactive sources should be kept in a shielded container when not in use, for example, a lead-lined box Radioactive materials should only be handled when wearing gloves, and with tongs to increase the distance from them It may be appropriate to wear protective clothing to prevent the body becoming contaminated The time that a radioactive source is being used for should be limited

Representing Transverse Waves

Transverse waves are drawn as a single continuous line, usually with a central line showing the undisturbed position The curves are drawn so that they are perpendicular to the direction of energy transferThese represent the peaks and troughs Transverse waves are represented as a continuous solid line

Ultraviolet

Ultraviolet is responsible for giving you a sun tan, which is your body's way of protecting itself against the ultraviolet When certain substances are exposed to ultraviolet, they absorb it and re-emit it as visible light (making them glow) This process is known as fluorescence Fluorescence can be used to secretly mark things using special ink - in fact, most bank notes have invisible fluorescent markings on them Fluorescent light bulbs also use this principle to emit visible light

Dangers of Ultraviolet

Ultraviolet is similar to visible light, except it is invisible to the human eye and carries a much higher energy If eyes are exposed to high levels of UV it can cause severe eye damage Good quality sunglasses will absorb ultraviolet, preventing it from entering the eyes Ultraviolet is ionising meaning it can kill cells or cause them to malfunction, resulting in premature ageing, and diseases such as skin cancer Sunscreen absorbs ultraviolet light, preventing it from damaging the skin

Calculations with vectors

Vectors are represented by an arrow The arrowhead indicates the direction of the vector The length of the arrow represents the magnitude

Visible

Visible light is the only part of the electromagnetic spectrum that the human eye can see The human eye can detect wavelengths from 750 nanometers (red light) up to 380 nanometers (violet light)

Changes of State

When a substance changes state, the number of molecules in that substance doesn't change and so neither does its mass The only thing that changes is its energy Changes of state are physical changes and so they are reversible

Alpha Decay Equation

When the alpha particle is emitted from the unstable nucleus, the mass number and atomic number of the nucleus changes The mass number decreases by 4 The atomic number decreases by 2

Applications of EM Waves Table (Ultraviolet)

security marking (fluorescence) fluorecent bulbs (energy efficient lamps) getting a suntan

Applications of EM Waves Table (Visible light)

seeing and taking photographs/videos fiber optic communications

Weight

Weight is the effect of a gravitational field on a mass Weight is defined as: The force acting on an object due to gravitational attraction Planets have strong gravitational fields Hence, they attract nearby masses with a strong gravitational force Because of weight: Objects stay firmly on the ground Objects will always fall to the ground Satellites are kept in orbit The weight of a body is equal to the product of its mass (m) and the acceleration of free fall (g)

Factors Affecting Floating & Sinking

Whether an object sinks or floats depends on the upthrust: If the upthrust on an object is equal to (or greater than) the object's weight, then the object will float If the upthrust is smaller than the weight then the object will sink The outcome also depends on the object's density: If it has a density less than the density of the fluid it is immersed in, the object will float If it has a density more than the density of the fluid it is immersed in, the object will sink This is because if the density of the object is greater than the density of the fluid, the object can never displace enough fluid to create an upthrust that will hold its weight up (and therefore sinks)

Density

Density is defined as: The mass per unit volume of a material Objects made from low density materials typically have a low mass Similarly sized objects made from high density materials have a high mass For example, a bag full of feathers is far lighter compared to a similar bag full of metal Or another example, a balloon is less dense than a small bar of lead despite occupying a larger volume Density is related to mass and volume by the following equation: Gases, for examples, are less dense than solids because the molecules are more spread out (same mass, over a larger volume) The units of density depend on what units are used for mass and volume: If the mass is measured in g and volume in cm3, then the density will be in g/cm3 If the mass is measured in kg and volume in m3, then the density will be in kg/m3 This table gives some examples of densities on common materials If a material is more dense than water (1000 kg/m3), then it will sink

Constant Speed on a Distance-Time Graph

Distance-time graphs also show the following information: If the object is moving at a constant speed How large or small the speed is A straight line represents constant speed The slope of the straight line represents the magnitude of the speed: A very steep slope means the object is moving at a large speed A shallow slope means the object is moving at a small speed A flat, horizontal line means the object is stationary (not moving)

List the liquids in order of lowest density to highst.

Ethyl Alcohol Olive Oil Water Liquid Soap Honey

What is friction in fluids?

Gases and liquids are known as fluids Fluids are different to solids because the particles in fluids can move around Friction acts on objects moving through gases and liquids as the particles collide with the object This type of friction is called drag Air resistance is a type of friction that slows the motion of an object Particles bump into the object as it moves through the air As a result, the object heats up due to the work done against the frictional forces

Interpreting Speed-Time graphs

If there is a change in an object's speed, then it is accelerating

Average Speed

In some cases, the speed of a moving object is not constant For example, the object might be moving faster or slower at certain moments in time (accelerating and decelerating) The equation for calculating the average speed of an object is: The formula for average speed (and the formula for speed) can be rearranged with the help of the formula triangle below:

Worked Example Diagram showing the moments acting on a balanced beam

In the above diagram: Force F2 is supplying a clockwise moment; Forces F1 and F3 are supplying anticlockwise moments Hence: F2 x d2 = (F1 x d1) + (F3 x d3)

Acceleration of Free Fall

In the absence of air resistance, all objects fall with the same acceleration This is called the acceleration of freefall (this is also sometimes called acceleration due to gravity) In the absence of air resistance, Galileo discovered that all objects (near Earth's surface) fall with an acceleration of about 9.8 m/s2 This means that for every second an object falls, its velocity will increase by 9.8 m/s The symbol g also stands for the gravitational field strength, and can be used to calculate the weight of an object using its mass: weight = mass × gravitational field strength W = mg

Motion of Falling Objects (without air resistance)

In the absence of air resistance, all objects falling in a uniform gravitational field, fall with the same acceleration, regardless of their mass So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for.

Mass

Mass is a measure of the quantity of matter in an object at rest relative to the observer Mass is a scalar quantity The SI unit for mass is the kilogram (kg) Consequently, mass is the property of an object that resists change in motion The greater the mass of an object, the more difficult it is to speed it up, slow it down, or change its direction A mass may sometimes be given in grams (g)1000 g = 1 kg1 g = 0.001 kg

Ose decides to take a stroll to the park. He finds a bench in a quiet spot and takes a seat, picking up where he left off reading his book on Black Holes. After some time reading, Ose realises he lost track of time and runs home. A distance-time graph for his trip is drawn below. a) How long does Ose spend reading his book? b) There are three sections labelled on the graph, A, B and C. Which section represents Ose running home? c) What is the total distance travelled by Ose?

Part (a) Ose spends 40 minutes reading his book The flat section of the line (section B) represents an object which is stationary - so section B represents Ose sitting on the bench reading This section lasts for 40 minutes - as shown in the graph below Part (b) Section C represents Ose running home The slope of the line in section C is steeper than the slope in section A This means Ose was moving with a larger speed (running) in section C Part (c) The total distance travelled by Ose is 0.6 km The total distance travelled by an object is given by the final point on the line - in this case, the line ends at 0.6 km on the distance axis. This is shown in the image below:

A Japanese bullet train decelerates at a constant rate in a straight line. The velocity of the train decreases from 50 m/s to 42 m/s in 30 seconds. (a) Calculate the change in velocity of the train. (b) Calculate the deceleration of the train, and explain how your answer shows the train is slowing down.

Part (a) Step 1: List the known quantities Initial velocity = 50 m/s Final velocity = 42 m/s Step 2: Write the relevant equation change in velocity = final velocity − initial velocity Step 3: Substitute values for final and initial velocity change in velocity = 42 − 50 = −8 m/s Part (b) Step 1: List the known quantities Change in velocity, Δv = − 8 m/s Time taken, t = 30 s Step 2: Write the relevant equation Step 3: Substitute the values for change in velocity and time a = −8 ÷ 30 = −0.27 m/s Step 4: Interpret the value for deceleration The answer is negative, which indicates the train is slowing down

Measuring Density (Vernier caliper)

Purpose- to measure objects up to around 15 cm in length Resolution- 0.01mm

Measuring Density (Micrometer)

Purpose- to measure objects up to around 3 cm in length Resolution- 0.001mm

Measuring Density (Displacement "Eureka" can)

Purpose- to measure the displacement of water of irregular objects

An experiment to measure the extension of a spring

Set up the apparatus as shown in the diagram A single mass (0.1 kg, 100g) is attached to the spring, with a pointer attached to the bottom, and the position of the spring is measured against the ruler The mass (in kg) and position (in cm) are recorded in a table A further mass is added and the new position measured The above process continues until a total of 7 masses have been added The masses are then removed and the entire process repeated again, until it has been carried out a total of three times, and averages can then be taken Once measurements have been taken: The force on the spring can be found by multiplying the mass on the spring (in kg) by 9.81 N/kg (the gravitational field strength) The extension of the spring can be found by subtracting the original position of the spring from each of the subsequent positions Finally, a graph of extension (on the y-axis) against force (on the x-axis) should be plotted

A distance-time graph is drawn below for part of a train journey. The train is travelling at a constant speed. Calculate the speed of the train.

Step 1: Draw a large gradient triangle on the graph and label the magnitude of the rise and run The image below shows a large gradient triangle drawn with dashed lines The rise and run magnitude is labelled, using the units as stated on each axes Step 2: Convert units for distance and time into standard units The distance travelled (rise) = 8 km = 8000 m The time taken (run) = 6 mins = 360 s Step 3: State that speed is equal to the gradient of a distance-time graph The gradient of a distance-time graph is equal to the speed of a moving object: Step 4: Substitute values in to calculate the speed speed = gradient = 8000 ÷ 360 speed = 22.2 m/s

A hiker walks a distance of 6 km due east and 10 km due north. Calculate the magnitude of their displacement and its direction from the horizontal.

Step 1: Draw a vector diagram Step 2: Calculate the magnitude of the resultant vector using Pythagoras' Theorem Resultant vector = 11.66 Step 3: Calculate the direction of the resultant vector using trigonometry Step 4: State the final answer complete with direction Resultant vector = 12 km 59° east and upwards from the horizontal

Calculate how long it took the runner to complete the lap

Step 1: Identify the start time for the lap The stopwatch was already at 0:55:10 when the runner started the lap Start time = 55.10 seconds (s) Step 2: Identify the finish time for the lap The stopwatch reads 1:45:10 at the end of the lap Finish time = 1 minute and 45.10 s Step 3: Convert the finish time into seconds 1 minute = 60 seconds Finish time = 60 s + 45.10 s Finish time = 105.10 s Step 4: Calculate the time taken to complete the lap The time taken to complete the lap = finish time − start time Time taken to complete lap = 105.10 s − 55.10 s Time taken to complete lap = 50 s

Worked Example Three shopping trolleys, A, B and C, are being pushed using the same force. This force causes each trolley to accelerate. Which trolley will have the smallest acceleration? Explain your answer.

Step 1: Identify which law of motion to apply The question involves quantities of force and acceleration, and the image shows trolleys of different masses, so Newton's second law is required: F = ma Step 2: Re-arrange the equation to make acceleration the subject a = F/m Step 3: Explain the inverse proportionality between acceleration and mass Acceleration is inversely proportional to mass This means for the same amount of force, a large mass will experience a small acceleration Therefore, trolley C will have the smallest acceleration because it has the largest mass

Worked Example A parent and child are at opposite ends of a playground see-saw. The parent weighs 690 N and the child weighs 140 N. The adult sits 0.3 m from the pivot. Calculate the distance the child must sit from the pivot for the see-saw to be balanced.

Step 1: List the know quantities Clockwise force (child), Fchild = 140 N Anticlockwise force (adult), Fadult = 690 N Distance of adult from the pivot, dadult = 0.3 m Step 2: Write down the relevant equation Moments are calculated using: Moment = force × distance from pivot For the see-saw to balance, the principle of moments states that Total clockwise moments = Total anticlockwise moments Step 3: Calculate the total clockwise moments The clockwise moment is from the child Momentchild = Fchild × dchild = 140 × dchild Step 4: Calculate the total anticlockwise moments The anticlockwise moment is from the adult Momentadult = Fadult × dadult = 690 × 0.3 = 207 Nm Step 5: Substitute into the principle of moments equation 140 × dchild = 207 Step 6: Rearrange for the distance of the child from the pivot dchild = 207 ÷ 140 = 1.48 m

Worked Example Calculate the depth of water in a swimming pool where a pressure of 20 kPa is exerted. The density of water is 1000 kg/m3 and the gravitational field strength on Earth is 9.8 N/kg.

Step 1: List the know quantities Pressure, p = 20kPa Density of water, p = 1000kg/m3 Gravitational field strength, g = 9.8N/kg Step 2 : List the relevant equation p = hpg Step 3: Rearrange for the height, h h = p/pg Step 4 : Convert any units 20 kPa = 200 000 Pa Step 5: Substitute in the values h = 20 000 = 2.0408 = 2.0m 1000 x 9.8

Planes fly at typical speeds of around 250 m/s. Calculate the total distance travelled by a plane moving at this average speed for 2 hours.

Step 1: List the known quantities Average speed = 250 m/s Time taken = 2 hours Step 2: Write the relevant equation Step 3: Rearrange for the total distance total distance = average speed × time taken Step 4: Convert any units The time given in the question is not in standard units Convert 2 hours into seconds: 2 hours = 2 × 60 × 60 = 7200 s Step 5: Substitute the values for average speed and time taken total distance = 250 × 7200 = 1 800 000 m

Worked Example: Liquid A has a density of 0.76 g/cm3 and liquid B has a density of 0.93 g/cm3. If the two liquids do not mix, which liquid will float on top of the other?

Step 1: List the known quantities Liquid A = 0.76 g/cm3 Liquid B = 0.93 g/cm3 Step 2: Determine which liquid has the lowest density The liquid with the lowest density will float on top of the liquid with the higher density 0.76 is less than 0.93 Therefore, liquid A has the lowest density Step 3: State your answer Liquid A will float on top of liquid B

Worked Example If there are no external forces acting on the car and it is moving at a constant velocity, what is the value of the frictional force, F?

Step 1: Recall Newton's first law of motion Newton's first law of motion states that objects will remain at rest, or move with a constant velocity unless acted on by a resultant force Step 2: Relate Newton's first law to the scenario Since the car is moving at a constant velocity, there is no resultant force This means the driving and frictional forces are balanced Step 3: State the value of the frictional force Frictional force, F = driving force = 3 kN

How to explain the difference between mass and weight using scalar and vectors in your answer

Step 1: Recall the definitions of a scalar and vector quantity Scalars are quantities that have only a magnitude Vectors are quantities that have both magnitude and direction Step 2: Identify which quantity has magnitude only Mass is a quantity with magnitude only So mass is a scalar quantityBlu might explain to his junior astronauts that their mass will not change if they travel to outer space Step 3: Identify which quantity has magnitude and direction Weight is a quantity with magnitude and direction (it is a force) So weight is a vector quantityBlu might explain that to his junior astronauts that their weight - the force on them due to gravity - will vary depending on their distance from the centre of the Earth

What does Hooke's law state?

The extension of a spring is proportional to the applied force FORCE = SPRING CONSTANT x EXTENSION F = kx Where: F is the force applied k is the spring constant x is the extension of the spring The spring constant is the force per unit extension The units are N/m The spring constant is a measure of how stiff the spring is Many other materials (such as metal wires) also obey Hooke's law Hooke's law is associated with the initial linear (straight) part of a force-extension graph Objects that obey Hooke's law will return to their original length after being stretched If an object continues to be stretched it can be taken past the limit of proportionality (sometimes called the elastic limit). At this point the object will no longer obey Hooke's law and will not return to its original length

A small object falls out of an aircraft. Choose words from the list to complete the sentences below:

The weight of an object is the product of the object's mass and the gravitational field strength. The weight force is due to the Earth's gravitational pull on the object's mass as it falls through a uniform gravitational field Part (b) When an object falls, initially it accelerates. The resultant force on the object is very large initially, so it accelerates This is because there is a large unbalanced force downwards (its weight) - the upward force of air resistance is very small to begin with Part (c) As the object falls faster, the force of friction acting upon the object increases. The force of air resistance is due to friction between the object's motion and collisions with air particles Collisions with air particles slow the object down, so air itself produces a frictional force, called air resistance (sometimes called drag) Part (d) Eventually the object falls at a steady speed when the force of friction equals the force of weight acting on it. When the upwards air resistance increases enough to balance the downwards weight force, the resultant force on the object is zero This means the object isn't accelerating - rather, it is moving at a steady (terminal) speed

Calculating Vectors Graphically

Vectors at right angles to one another can be combined into one resultant vector The resultant vector will have the same effect as the two original ones To calculate vectors graphically means carefully producing a scale drawing with all lengths and angles correct This should be done using a sharp pencil, ruler and protractor Follow these steps to carry out calculations with vectors on graphs Choose a scale which fits the pageFor example, use 1 cm = 10 m or 1 cm = 1 N, so that the diagram is around 10 cm high Draw the vectors at right angles to one another Complete the rectangle Draw the resultant vector diagonally from the origin Carefully measure the length of the resultant vector Use the scale factor to calculate the magnitude Use the protractor to measure the angle

Vectors

Vectors have both magnitude and direction Velocity, for instance, is a vector since it is described with both a magnitude and a direction When describing the velocity of a car it is necessary to mention both its speed and the direction in which it is travelling For example, the velocity might be 60 km per hour (magnitude) due west (direction) Distance is a value describing only how long an object is or how far it is between two points - this means it is a scalar quantity Displacement on the other hand also describes the direction in which the distance is measured - this means it is a vector quantity For example, a displacement might be 100 km north

Circular Motion

Velocity is a vector quantity, and the velocity of an object is its speed in a given direction When an object travels along a circular path, its velocity is always changing The speed of the object moving in a circle might be constant - that is, it is travelling the same distance every second However, the direction of travel is always changing as the object moves along the circular path This means that an object moving in circular motion travels at a constant speed but has a changing velocity The image below shows an example of a famous object that moves in a circular path with a constant speed but changing direction: The International Space Station's velocity is always changing - it whizzes around the Earth at a constant speed of about 7660 m/s but is always changing direction When a force acts at 90 degrees to an object's direction of travel, the force will cause that object to change direction When the two cars collide, the first car changes its direction in the direction of the force If the force continues to act at 90 degrees to the motion, the object will keep changing its direction (whilst remaining at a constant speed) and travel in a circle This is what happens when a planet orbits a star (or satellite orbits a planet) The Moon is pulled towards the Earth (at 90 degrees to its direction of travel). This causes it to travel in a circular path The force needed to make something follow a circular path depends on a number of factors: The mass of the object A greater mass requires a greater force when the speed and radius are constant The speed of the object A faster-moving object requires a greater force when the mass and radius are constant The radius of the circle A smaller radius requires a greater force to keep the speed and radius constant