Physics concepts - P12 Electricity

P12.6: 2) Demonstrate understanding of the use of circuit-breakers.

- A circuit breaker is a safety device that forces a circuit to open (switch off) when an extremely high level of current flows through the circuit. 1. Electricity flows in the circuit breaker through the metal contacts. 2. If an extremely high current flows through the circuit breaker, the electromagnet gets stronger and pulls the iron catch towards it. 3. Causes spring to pull the metal contacts apart, causing the circuit to open/break.

P12.2: 2) State that there are positive and negative charges.

- 2 insulating materials are rubbed together (in this case a carpet and the balloon), friction causes electrons on one material to be rubbed off and left stranded on the other. - Normally, objects are neutrally charged, meaning that the atoms have an equal number of protons and electrons. However, when we rub two insulating materials together, what we end up is one material is left too much electrons, and as result becomes negatively charged due to more electrons than protons. - Conversely, the other object is left with more protons than electron (loses it). Hence, it becomes positively charged. - Due to the nature of water molecules, they are polar, meaning that their molecules have a positive and negative charged ends, much like a magnet. They are very weakly attracted to charged objects.

P12.2: 3) Describe an electric field as a region in which an electric charge experiences a force

- An electric field is created when an electrically charged object is placed near another charged/polar object - Creates a force of electrostatic attraction between the two. - Water bends towards the negatively charged balloon because: - Positive pole of water molecules=attracted to the negatively charged ions of the balloon. - Positive pole of water molecule: 1. aligns 2. rotates towards the balloon and is pulled towards it. - However: Water molecules have a negative pole as well, so shouldn't it repel each other as well? - The negative poles of the water molecule are repelled by the negatively charged ions of the balloon. - However, the water molecules still bend towards the stream. - Positive poles of the water molecules are closer to the balloon since they are attracted to it, the force of attraction between the positive ends is stronger than the repulsion between the negative ends.

P12.2: 5) Distinguish between electrical conductors and insulators and give typical examples.

- Conductors are materials in which an electric current can flow freely. - copper, aluminum, gold, and silver - Insulators oppose electrical current and make poor conductors. - glass, air, plastic, rubber, and wood.

P12.3: 3) Demonstrate understanding that a current is a rate of flow of charge and recall and use the equation I=Q/t.

- Current is the rate of flow of charge in a given point of a circuit - I = Q/t 1. I = Current measured in amps 2. Q = the charge carried measured in coulombs 3. T = Time

P12.6: 1) Identify electrical hazards including • damaged insulation, • overheating of cables, • damp conditions.

- Damaged Insulation: 1. In a circuit, insulation= the plastic sheath that covers wires. If you have damaged insulation, it means that metal wires inside the cable are exposed. 2. The potential dangers of damaged insulation could be that if a person touches exposed wire, they could be electrically shocked, which may lead to death. - Overheating of cables: 1. When you run a extremely high current through a cable, you run a risk of overheating the wire. This is because you are supplying too much energy and this causes to wire to heat up. 2. If the wires overheat, this could lead to electrical fires. Damp conditions: 1. Since water is a conductor, during damp situations such as inside a bathroom, electricity from the electrical appliance may electrocute nearby people through the conductive water. 2. Also dry skin itself is an electrical resistance and would act as an insulating layer with high resistance, and if the skin is dampened, the resistance of the skin will fall, resulting a higher chance of the person being electrocuted.

P12.3: 6) Demonstrate understanding that e.m.f. is defined in terms of energy supplied by a source in driving charge round a complete circuit.

- Electro-motive force (e.m.f) = voltage (potential) that a battery will supply. - Driving force that gives the electrons the energy to move around the circuit. - For example, a 12V battery will provide a e.m.f of 12V.

P12.2: 1) Describe and interpret simple experiments to show the production and detection of electrostatic charges.

- Electrostatic Attraction can be reproduced and observed in a simple experiment: 1. Get a balloon. 2. Inflate it. 3. Rub the balloon quickly on any dry surface e.g. a carpet. 4. Go to the nearest tap 5. Turn it on. 6. Place the balloon close to but not touching the running water. - You should see that the water bends towards the balloon.

P12.3: 5) Distinguish between the direction of flow of electrons and conventional current.

- In an electrical circuit, the flow of electrons go from (-) pole of the battery to the (+) pole. - Conventional current flows in opposite direction of the flow of electron, from (+) pole of the battery to the (-) pole. - Because the battery provides an electro-motive force (e.m.f) that pushes the electrons forward, making them do work.

P12.3: 4) Use the term potential difference (p.d.) to describe what drives the current between two points in a circuit.

- Moving an electric current through a metal wire=work/energy. - Run electricity through a wire=HOT. - Electric potential energy carried by current is used to push current through the wire and the energy is lost as heat. Therefore, potential represents how much energy there is to drive a current through the wire and is measured in volts (v).

P12.6: 3) Demonstrate understanding of the use of fuses.

- Protect components in a circuit from overheating by breaking circuit. - Integrated into circuit they are meant to protect. - A high level of current flowing through the circuit causes the wires inside the circuit to heat up. - Inside the fuse is a metal wire with a low melting point. - Metal wire inside the fuse may melt=fuse melts and therefore the circuit to break.

P12.4: 3) Describe an experiment to determine resistance using a voltmeter and an ammeter.

- Set up an ammeter somewhere in the series circuit: this will give you the amount of current flowing in the circuit. - Now, set up a voltmeter in parallel to the object, in this case a light bulb, to find the potential difference across it. - Using the equation R = V/I , we can find the resistance. - If the light bulb has a potential difference of 4V, and the circuit has a current of 2A, then the resistance is: 4/2 = 2 Ohms (Ω)

P12.2: 4) State that unlike charges attract and that like charges repel.

- Unlike (opposite) charges attract. ( + ) → ← ( - ) - Like (same) charges repel. ( - ) ← → ( - ) - A good analogy would be magnets. Think of magnets.

P12.4: 2) Recall and use the equation R=V/I

- When you need to calculate resistance, Ohm's law states that: R = V/I - Resistance (Ω) = Voltage (V) / Current (I) - For example, a light bulb has a potential resistance of 3 volts. If a current of 0.6 amps is flowing through the lightbulb, what is the resistance? R = V/I R = 3 / 0.6 Resistance = 5 Ω

P12.1: 3) Use and describe the use of an ammeter and a voltmeter.

Ammeter: - Is a device used to measure the amount of current flowing through the circuit (in amps) - Has to connected in series to the circuit - Think of Assault Course analogy Voltmeter: - Is a device used to measure the potential difference between two points in a circuit. - Has to be connected in parallel to the component you want to measure. - Think of Supermarket analogy

P12.1: 2) What is charge measured in?

Charge is measured in coulombs (C).

P12.3: 2) Why is there current in metals?

Current in metals is due to a flow of electrons.

P12.3: 1) State that current is related to the flow of charge.

Current: is the flow of electrical charge within the circuit.

P12.1: 1) Demonstrate understanding of current, potential difference, e.m.f. and resistance, and use With their appropriate units. (Remember assault course analogy)

Electric Current (speed of soldiers): - Is the flow of electric charge within a circuit. - Is measured in amperes or amps (A). - Represents how much electric charge is passing a single point in the circuit - Does not run out in a circuit i.e. current is the same at the beginning and end of a circuit. Potential Difference (energy after each obstacle): - Difference in potential between two points of a circuit. - Potential represents how much energy (joules per coulomb) there is to drive a current through the wire and is measured in volts (v) E.M.F (Mars Bars): - Electro-motive force (e.m.f) is the voltage (potential) that a battery will supply. - It is the driving force that gives the electrons the energy to move around the circuit. Resistance (Obstacles): - Is a measure of how difficult it is to push a current through a circuit. - Is measured in Ohms (Ω)

P12.5: 1) Recall and use the equations P=IV and E=IVt

P= IV (Unit: Watts) P is power, I is Electric Current (measured in Amps), and V is Potential difference (Voltage, measured in Volts). Units for power is Watts. This is also known as Joule's Law. E= I V t (Units: Joules) E= Energy I= Electric Current t= time (sec)

(?) P12.4: 4) Recall and use quantitatively the proportionality between resistance and length, and the inverse proportionality between resistance and cross-sectional area of a wire.

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P12.4: 1) State that resistance = p.d./current and understand qualitatively how changes in p.d. or resistance affect current.

Since resistance = potential difference / current: ↑ in Voltage = ↑ in resistance ↑ in Current = ↓ in resistance