AS/2 OCR Physics- The Motherload.

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Doppler equation

(∆λ)/λ ≈ (∆f)/f ≈ v/c Where 'λ' is the source wavelength, '∆λ' is the change in wavelength recorded by the observer, 'f' is the source frequency, '∆f' is the change in frequency recorded by the observer, 'v' is the magnitude of the relative velocity between the source and the observer, and 'c' is the speed of light through a vacuum (3.00x10⁸ms⁻¹)

Electronvolt

A derived unit of energy used for subatomic particles and photons, defined as the energy transferred to or from an electron when it passes through a potential difference of 1 volt; 1 eV is equivalent to 1.60x10⁻¹⁹J

Kilowatt-hour

A derived unit of energy, most often associated with paying for electrical energy, symbol kWh (1kWh=3.6MJ). Energy in kWh can be calculated by multiplying the power kW by the time in hours

I-V characteristic

A description of the relationship between the electric current in a component and the potential difference across it -- in most cases this is usually in the form of a simple graph of I against V

Cloud chamber

A detector of ionising radiation consisting of a chamber filled with air saturated with vapour at a very low temperature so that droplets of liquid condense around ionised particles left along the path of radiation

Electricity meter

A device that measures the electrical energy supplied in kWh to a house from the grid

Cell

A device that transfers chemical energy into electrical energy

Electron gun

A device that uses a large accelerating potential difference to produce a narrow beam of electrons

Velocity selector

A device that uses both electric and magnetic fields to select charged particles of specific velocity

Ultrasound transducer

A device used both to generate and to receive ultrasound, which changes electrical energy into sound and sound into electrical energy

Ammeter

A device used to measure electric current-- it must be placed in series and ideally have zero resistance

Voltmeter

A device used to measure potential difference -- it must be placed in parallel across the components and ideally have an infinite resistance

Gold-leaf electroscope

A device with a metallic stem and a gold leaf that can be used to identify and measure electric charge -- a device that was historically used as a voltmeter for measuring large voltages

Free-body diagram

A diagram that represents the forces acting on a single object

Eneru level

A discrete (quantised) amount of energy that an electron within an atom is permitted to possess

Optical fibre

A fibre made of glass designed with a varying refractive index in order to totally internally reflect pulses of visible or infrared light travelling through it

Gravitational field

A field created around any object with mass, extending all the way to infinity, but diminishing as the distance from the centre of mass of the object increases

Centripetal force

A force that keeps a body moving with a constant speed in a circular path

Restoring force

A force that tries to return a system to its equilibrium position

Loading curve

A force-extension graph

Lepton

A fundamental particle or antiparticle that is not affected by the strong nuclear force -- for example, an electron

Elementary perticle

A fundemental particle

Coupling gel

A gel with acoustic impedance similar to that of skin smeared onto the transducer and the patient's skin before an ulstrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters the patients body

Diffraction grating

A glass or plastic slide on which as many as 1000 lines in a millimetre are ruled, at a spacing that diffracts visible wavelengths of light

Force-extension graph

A graph of force against extension (or compression), with the area under the graph equal to the work done on the material

Force-time graph

A graph of net force against time, with the area under the graph equal to the impulse

Wave profile

A graph showing the displacement of the particles in the wave against the distance along the wave

Hertzsprung-Russell diagram

A graph showing the relationship between the luminosity of stars in out galaxy (on the y axis) and their average surface temperature (on the x axis, with the temperature increasing from right to left)

Uniform gravitational field

A gravitational field in which field lines are parallel and the value for g remains constant

Red supergiant

A huge star in the last stages of its life before it 'explodes' in a supernova

Dark energy

A hypothetical form of energy that fills all of space and would explain the accelerating expansion of the Universe

Dark matter

A hypothetical form of matter spread throughout the galaxy that neither emits or absorbs light- it could explain the differences between the predicted and observed velocities of stars in galaxies

Neutrino

A lepton (a fundamental particle) that carries no charge and may have tiny mass, less than a millionth the mass of an electron

Spectral line

A line in an emission line spectrum or absorption line spectrum at a specific wavelength

Wavefront

A line of points in phase with each other in a wave, perpendicular to the direction of energy transfer

Isotherm

A line on a pressure-volume graph that connects points at the same temperature

Ray

A line representing the direction of energy transfer of a wave, perpendicular to the wavefronts

Kepler's second law of planetary motion

A line segment connecting a planet to the Sun sweeps out equal areas during equal intervals of time

Electrolyte

A liquid containing ions that are free to move and so to conduct electricity

Hysteresis loop

A loop-shaped plot obtained when, for example, loading and unloading a material produce different deformations

Fiducial marker

A marker for a point used as a fixed basis for measurement or comparison

Point mass

A mass with negligible volume

Strong material

A material with a large value for the ultimate tensile strength

Semiconductor

A material with a lower number density than a typical conductor, for example silicon

Attenuation coefficient

A measure of absorption of X-ray photons by a substance, also known as absorption coefficient- SI unit m⁻¹

Absorption coefficient

A measure of the absorption of X-ray photons by a substance, also known as attenuation coefficient- SI uni m⁻¹

Amount of substance

A measure of the amount of matter in moles

Eccentricity

A measure of the elongation of an ellipse

Target metal

A metal with high melting point used for the anode in an X-ray tube, for example tungsten

Carbon dating

A method for determining the age of organic material, by comparing the activities, or the ratios, of carbon-14 to carbon-12 nuclei of the dead material of interest and similar living material

Crystallography

A method for determining the structure of a substance by studying the interference patterns produced by the waves passing through a crystal of the substance

Arcminute

A minute of arc; 1°=60 arcminutes

Fleming's left hand rule

A mnemonic for the direction of force experienced by a current-carrying wire placed perpendicular to the external magnetic field: on the left hand, the first finger gives the direction of the external magnetic field, the second finger gives the direction of current, and the thumb gives the direction of motion (force) of the wire

Ideal gas

A model of gas including assumptions that simplify the behaviour of real gases

Kinetic model

A model that describes all substances as made of atoms, ions or molecules, arranged differently depending on the phase of the substance

Conventional current

A model used to describe electric current in a circuit -- conventional current travels from positive to negative -- it is the direction in which positive charges would travel

Compression (waves)

A moving region in which the medium is denser or has a higher pressure than the surrounding medium

Rarefaction (waves)

A moving region in which the medium is less dense or has less pressure than the surrounding medium

Cathode

A negatively charged electrode

Anion

A negatively charged particle, one which is attracted to an anode

Beta decay

A neutron in an unstable nucleus decays into a proton, an electron or an antineutrino (β⁻ decay), or a proton into a neutron, a positron and an electron neutrino (β⁺ decay)

Thermal neutron

A neutron is a fission reactor with mean kinetic energy similar to the thermal energy of particles in the reactor core - also known as a slow neutron

Daughter nucleus

A new nucleus formed following a radioactive decay

Parent nucleus

A nucleus before the occurrence of radioactive decay

Couple

A pair of equal and opposite forces acting on a body but not in the same straight line

Nucleon

A particle in the nucleus of an atom, either a proton or a neutron

Hadron

A particle or antiparticle that is affected by the strong nuclear force, and, if charged, by the electromagnetic force - for example, a proton

Fundamental particle

A particle that has no internal structure and hence cannot be split into smaller particles

Charge carrier

A particle with a charge that moves through a material to form an electric current- e.g., an electron in a metal wire

Interference pattern

A pattern of consecutive and destructive interference formed as waves overlap

Inflation

A phase of astonishing acceleration of the expansion of the Universe thought to have occurred 10⁻³⁵s after the Big Bang

Phase

A phase of matter is its state (solid, liquid, or gas)

Superconductivity

A phenomenon in which the resistivity of a material falls to almost zero when the material is cooled below a certain temperature

Electric charge

A physical property, symbol 'q' or 'Q', either positive or negative, measured in coulombs 'C' or as a relative charge

X-ray tube

A piece of equipment that produces X-ray photons by firing electrons from a heated cathode across a large p.d. in an evacuated tube - X-ray photons are produced when the electrons are decelerated by hitting the target metal of the anode

Solar system

A planetary system consisting of a star and at least one planet in orbit around it - our own Solar System contains the Sun and all objects that orbit it

Pivot

A point at which a body can rotate

Yield point

A point on a stress-strain graph beyond which the deformation is no longer entirely elastic

Centre of mass

A point through which any externally applied force produces straight-line motion but no rotation

Negative temperature coefficient (NTC)

A relationship in which a variable decreases as the temperature increases, for example the resistance of NTC thermistors

Elastic deformation

A reversible change in the shape of an object due to a compressive or tensile force -- removal of stress or force will return the object to its original shape and size (no permanent strain)

Geostationary satellite

A satellite that remains in the same position relative to a spot on the Earth's surface, by orbiting in the direction of the Earth's rotation over the equation with a period of 24 hours

Absolute scale of temperature

A scale for measuring temperature based on absolute zero and the triple point of pure water, with the gradations equal in size to those of the Celsius scale;unit kelvin (K)

Thermodynamic scale of temperature

A scale for measuring the temperature based on absolute zero and the triple point of pure water, with gradations equal in size to those of the Celsius scale; unit kelvin (K)

Arcsecond

A second of arc; 1 arcminute = 60 arcseconds

Diode

A semiconductor component that allows current only in one particular direction

Emission line spectrum

A set of specific frequencies of electromagnetic radiation, visible as bright lines in spectroscopy, emitted by excited atoms as their electrons make transitions between higher and lower energy states, losing the corresponding amount of energy in the form of photons as they do so - every element has a characteristic line spectrum

Absorption line spectrum

A set of specific frequencies of electromagnetic radiation, visible as dark lines in an otherwise continuous spectrum on spectroscopy. They are absorbed by atoms as their electrons are excited between energy states by absorbing the corresponding amount of energy in the form of photons- every element has a characteristics line spectrum

Conical pendulum

A simple pendulum that, instead of swinging back and forth, rotates in a horizontal circle at a constant speed

Relative charge

A simplified measurement of the electric charge of a particle or object, measures as multiples of the elementary charge

Resultant vector

A single vector that has the same effect as two or more vectors added together

Comet

A small, irregular body made of ice, dust, and small pieces of rock in an (often highly eccentric elliptical) orbit around the Sun - as they approach the Sun, some comets develop spectacular tails

Wave source

A source of waves, such as light or sound - the object moving relative to an observer of the Doppler effect

Continuous spectrum

A spectrum in which all visible frequencies or wavelengths are present (a heated solid metal such as lamp filament will produce this type of spectrum)

Velocity

A vector quantity equal to the rate of change of displacement

White dwarf

A very dense star formed from the core of a red giant, in which no fusion occurs

Protostar

A very hot, very dense sphere of condensing dust and gas that is on the way to becoming a star

Fundamental mode of vibration

A vibration at the fundamental frequency

Longitudinal wave

A wave in which the medium is displaced in the same line as the direction of energy transfer -- oscillations of the medium particles are parallel to the direction of the wave travel

Transverse wave

A wave in which the medium is displaced perpendicular to the direction of energy transfer - the oscillations of medium particles are perpendicular to the direction of travel of the wave

Progressive wave

A wave in which the peaks and troughs, or compressions and rarefactions, move through the medium as energy is transferred

Standing / stationary wave

A wave that remains in a constant position with no net transfer of energy and is characterised by its nodes and antinodes

Harmonic

A whole-number multiple of the fundamental frequency

Prefix

A word or letter placed before another one, for example 5.0km is 5.0x10³m

Kinetic theory of matter

All substances are made of atoms, ions or molecules, arranged differently depending on the phase of substance

Mass

Amount of matter, a base quantity measured in kilograms, kg

Black body

An idealised object that absorbs all the electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution of wavelengths at a specific temperature.

Normal

An imaginary line perpendicular to a surface such as the boundary between one medium and another (e.g. air and glass)

Centre of gravity

An imaginary point at which the entire weight of an object appears to act

Oscilloscope

An instrument that displays an electrical signal as a voltage against time trace on a screen

Ionic solution

An ionic compound dissolved in a liquid to form an electrolyte

Plastic deformation

An irreversible change in the shape of an object due to a compressive or tensile force -- removal of the stress of the force produces permanent deformation

Closed system

An isolated system that has no interaction with its surroundings

Planet

An object in orbit around a star with a mass large enough for its own gravity to give it a round shape, that undergoes no fusion reactions, and that has cleared its orbit of most other objects

Projectile

An object that is thrown or propelled on the surface of the Earth

Damping

An oscillation i damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations

Forced oscillation

An oscillation in which a periodic driver force is applied to an oscillator

Isochronous oscillator

An oscillator that has the same period regardless of amplitude

c

Centi,10⁻²

Loading (electrical circuits)

Connecting a component or a device across the terminals of a source of e.m.f. or across another component

Heavy damping

Damping that occurs when the damping forces are large and the period of the oscillations increases slightly with the rapid decrease in amplitude

Light damping

Damping that occurs when the damping forces are small and the period of the oscillations is almost unchanged

d

Deci, 10⁻¹

Electromotive force (e.m.f)

Defined as the energy transferred from chemical to electric energy per unit charge

Potential difference (p.d.)

Defined as the energy transferred from electrical energy to other forms (heat, light, etc.) per unit charge

Polymeric

Description of a material comprising of long-chain molecules, such as rubber, which may show large strains

Plane polarised

Description of a transverse wave in which the oscillations are limited to only one plane

Unpolarised

Description of a transverse wave in which the oscillations occur in many places

Partially polarised

Description of a transverse wave in which there are more oscillations in one particular plane, but the wave is not completely plane polarised-- occurs when transverse waves reflect off a surface

Breaking distance

Distance travelled by a vehicle from the time the brakes are applied until the vehicle stops

Photoelectric effect equation

Einstein's equation relating the energy of a photon, the work function of a metal, and the maximum kinetic energy of any emitted photoelectrons: hf=φ+KE(max)

Infrared waves

Electromagnetic waves, with wavelengths from 10⁻³m to 7x10⁻⁷m

Ultraviolet

Electromagnetic waves, with wavelengths from 4x10⁻⁷m to 10⁻⁸m

Visible light

Electromagnetic waves, with wavelengths from 4x10⁻⁷m to 7x10⁻⁷m

Photoelectrons

Electrons emitted from the surface of metal by the photoelectric effect

Principle of moments

For a body in rotational equilibrium, the sum of the anticlockwise moments about a point is equal to the sum of the clockwise moments about the same point

Right-hand grip rule

For a current-carrying wire, the thumb points in the direction of the conventional current, and the direction of the field is given by the direction in which the fingers of the right hand would curl around the wire

Triple point

For a given substance, one specific of that substance can exist in thermodynamic equilibrium

Node

For a stationary wave, a point where the amplitude is always zero

G

Giga, 10⁹

Gas pressure

In stars, the pressure of the nuclei in the star's core pushing outwards and counteracting the gravitational force pulling the matter in the star inwards

Parallel (vectors)

In the same line and direction

Antiparallel (vectors)

In the same line but opposite directions

Beta radiation

Ionising radiation consisting of fast-moving electrons (β⁻) or (β⁺) emitted from unstable nuclei, with a charge of -e or +e respectively

Gamma radiation

Ionising radiation consisting of high-energy photons, with wavelengths less than about 10⁻¹³m, which travel at the speed of light

Alpha radiation

Ionising radiation consisting of particles comprising two protons and two neutrons (a helium nucleus), with a charge of +2e

Microwaves

Long-wavelength electromagnetic waves, with wavelengths from 10⁻¹m to 10⁻³m

Radio waves

Long-wavelength electromagnetic waves, with wavelengths greater than 10⁻¹m

Standard form

Mathematical notation in which a number is shown with the decimal point is placed after the first digit, followed by x10 raised to the appropriate power

M

Mega, 10⁶

μ

Micro, 10⁻⁶

m

Milli, 10⁻³

n

Nano, 10⁻⁹

Induced fission

Nuclear fission occurring when a nucleus becomes unstable on absorbing another particle (such as a neutron)

Isotopes

Nuclei of the same element that have the same atomic numbers (number of protons) but different nucleon numbers (numbers of neutrons)

k

Kilo, 10³

Atomic mass unit

One atomic mass unit (1u) is one-twelfth the mass of a neutral carbon-12 atom.

Strong nuclear force

One of four fundamental forces in nature, acting on hadrons and holding nuclei together

Weak nuclear force

One of four fundamental forces in nature, responsible for inducing beta-decay within unstable nuclei

Base unit

One of seven units that form the building blocks of the SI system

Component

One of the two perpendicular vectors obtained by resolving a vector

Positive (charge)

One type of electric charge -- positively charged objects attract negatively charges ones, and repel other positive charges

Negative (charge)

One type of electric charge; negatively charged objects attract positively charged ones, and repel other negative charges

Simple harmonic motion

Oscillating motion for which the acceleration of the object is directly proportional to its displacement and is directed towards some fixed point - characterised by the equation a=ω²x

Superposition (waves)

Overlap of two waves at a point in space

P

Peta, 10¹⁵

P-waves

Primary waves- longitudinal waves that travel through the Earth from an earthquake

Control rods

Rods made of a material whose nuclei readily absorb neutrons (commonly boron or cadmium), which can be moved to ensure that exactly one slow neutron survives per fission reaction or to completely stop the fission raction

S-waves

Secondary waves: transverse waves that travel through the Earth from an earthquake

X-rays

Short wavelength electromagnetic waves, with wavelengths from 10⁻⁸m to 10⁻¹³m, which can be used in medical imaging

Gamma rays

Short-wavelength electromagnetic waves, with wavelengths from 10⁻¹⁰m to 10⁻¹⁶m

Resolving a vector

Splitting a vector into two component vectors perpendicular to each other

Kelvin

The SI base unit of the absolute (thermodynamic) scale of temperature

Stiffnes

The ability of an object to resist deformation

Centripetal acceleration

The acceleration of any object travelling in a circular path at constant speed, which always acts towards the centre of the circle

Mole

The amount of substance that contains as many elementary entities as there are atoms in 0.012kg (12g) of carbon-12

Angle of reflection

The angle between the direction of travel of a reflected wave ant the normal at a boundary between two medias

Angle of incidence

The angle between the direction of travel of an incident wave and the normal at a boundary between two media.

Critical angle

The angle of incidence at the boundary between two media that will produce an angle of refraction of 90°

Law of reflection

The angle of incidence is equal to the angle of reflection

Parallax angle

The angle of the apparent shift in the position of a relatively close star against the backdrop of much far more distant stars as the Earth makes a quarter an orbit around the Sun

Radian

The angle substituted by a circular arc with a length equal to the radius of a circle (approximately 57.3°)

Antiparticle

The antimatter counterpart of a particle, with the opposite charge to the particle (if the particle has charge) and exactly the same rest mass as the particle

Positron

The antiparticle of the electron

Impulse

The area under a force-time graph -- the product of force and the time for which the force acts

Cosmological principle

The assumption that, when viewed on a large enough scale, the Universe is homogeneous and isotropic, and the laws of physics are universal

Proton number

The atomic number, that is, the number of protons in a nucleus- symbol Z

Quantisation

The availability of some quantities, such as energy or charge, only in certain discrete values

Half-life

The average time it takes for half the number of active nuclei in a sample of an isotope to decay

Mean drift velocity

The average velocity of electrons as they move through a wire, symbol 'v', unit ms⁻¹

Ampère

The base SI unit of electric current, symbol A, defined as the current flowing in two parallel wires in a vacuum 1m apart such that there is a n attractive force of 2.0 x 10⁻⁷ N per metre length of wire between them

Binding energy per nucleon

The binding energy divided by the number of protons and neutrons in the nucleus; the greater the binding energy per nucleon, the more tightly bound are the nucleons within the nucleus

Quantum mechanics

The branch of physics dealing with phenomena on the very small scale, often less than the size of an atom

Gravitational potential energy

The capacity for doing work as a result of an object's position in a gravitational field

Energy

The capacity for doing work, measured in joules, J

Refraction

The change in direction of a wave as it changes speed when it passes from one medium to another

Reflection

The change in the direction of a wave at a boundary between two media, so that the wave remains in the original medium

Average velocity

The change in the displacement ∆t; ∆s / ∆t

Doppler effect

The change in the frequency and wavelength of waves received from an object moving relative to an observer compared with what would be observed without relative motion

Capacitance

The charge stored per unit of potential difference across a capasitor

Perihelion

The closest point to the Sun in an orbit

Annihilation

The complete destruction of a particle and its antiparticle in an interaction that releases energy in the form of identical photons

Gravitational constant, G

The constant in Newton's law of gravitation F=(GMm)/r², with a value determined from the experiment of 6.67x10⁻¹¹Nkg⁻²m²

Molar gas constant

The constant in the equation of the state of an ideal gas- symbol 'R', 8.31J⁻¹mol⁻¹

Terminal velocity

The constant speed reached by an object when the drag force (and upthrust) is equal to the weight of the object

Stephan constant

The constant σ in Stephan's law, : L=4πr²σT⁴, relating the luminosity, L, of a star to its surface area, 4πr², and its absolute surface temperature T: σ=5.67x10⁻⁸Wm⁻²K⁻⁴

Brownian motion

The continuous random motion of small particles suspended in a fluid, visible under a microscope

Standard model

The current theory of particle physics that deals with elementary particles (quarks, electrons, etc.) and their interactions

Compression

The decrease in length of an object when a compressive force is exerted on it

Attenuation

The decrease in the intensity of electromagnetic radiation as it passes through matter and/or space

Coulomb

The derived SI unit of electrical charge, symbol C; 1 coulomb of electrical charge passes a point in 1 second when there is an electrical current of 1 ampère, 1C=1As

Volt

The derived SI unit of potential difference and electromotive force, symbol V, defined as the energy transferred to or from the charges - 1V is the p.d. across the component when 1J of energy is transferred over 1C passing through the component

Ohm

The derived SI unit of resistance, symbol Ω -- defined as the resistance of a component that has a potential difference of 1V per unit ampere

Phase difference

The difference between the displacements of particles along a wave, or the difference between the displacements of particles on different waves, measured in degrees or radians, with each complete cycle or difference of one wavelength representing 360° or 2π radians

Mass defect

The difference between the mass of a nucleus and the mass of its completely separated constituent nucleons

Phase difference (for oscillating motion)

The difference in displacement between two oscillating objects or the displacement of an oscillating object at different times - symbol φ

Path difference

The difference in the distance travelled by two waves from their source to a specific point

Lenz's law

The direction of the induced e.m.f or current is always such as to oppose the change producing it

Parsec

The distance at which a radius of one AU subtends an angle of one arcsecond

Displacement (waves)

The distance from the equilibrium position in a particular direction -- displacement is a vector, so it has a positive or negative value`

Thinking distance

The distance travelled by a vehicle from when the driver first perceives a need to stop to when the breaks are applied

Light-year

The distance travelled by light in a vacuum in a time of one year (9.46x10¹⁵m)

Wave speed

The distance travelled by the wave per unit time

Displacement

The distance travelled in a particular direction -- it is a vector with magnitude and direction

Maxwell-Boltzmann distribution

The distribution of the speeds of particles in a gas

Air resistance

The drag or resistive force experienced by objects moving through air.

Elementary charge

The electric charge equivalent to the charge of a proton, 1.60x10⁻¹⁹C; symbol 'e'

Thermionic emission

The emission of electrons from the surface of a hot metal wire

Photoelectric effect

The emission of photoelectrons from a metal surface when electromagnetic radiation above a threshold frequency is incident on the metal

Kinetic energy

The energy associated with an object as a result of its motion

Ground state

The energy level with the most negative value possible for an electron within an atom - the most stable energy state of an electron

Specific heat capacity

The energy required per unit mass to change the temperature by 1K (or 1°C); unit Jkg⁻¹K⁻¹

Specific latent heat

The energy required to change the phase per unit mass while at constant temperature- symbol L

Specific latent heat of fusion

The energy required to change unit mass of a substance from solid to liquid while at a constant temperature - Symbol L(v)

Specific latent heat of vaporisation

The energy required to change unit mass of a substance from solid to liquid while at a constant temperature - symbol L(f)

Elastic potential energy

The energy stored in an object because of its deformation

Tensile strain

The extension per unit length, a dimensionless quality

Strain

The extension per unit length, a dimensionless quantity

Hooke's law

The force applied is directly proportional to the extension of the spring unless the limit of proportionality is exceeded

Newton's law of gravitation

The force between two point masses is directly proportional to the product of the masses and inversely proportional to the square of the separation between them: F=-(GMm)/r₂

Normal contact force

The force exerted by a surface on an object, which acts perpendicularly to the surface

Pressure

The force exerted per unit cross-sectional area, measured in pascals, Pa

Electric field streingth

The force experienced per unit positive charge at that point

Stress

The force per unit cross-sectional area, measured in Pa

Tensile stress

The force per unit cross-sectional area, measured is Pa

Natural frequency

The frequency of a free oscillation

Driving frequency

The frequency with which the periodic driver force is applied to a system in forced oscillation.

Electromagnetic spectrum

The full range of frequencies of electromagnetic waves, from gamma rays to radio waves

Aphelion

The furthest point from the sun in an orbit

Hubble constant

The gradient of a best-fit line for a plot of recessional speed against distance from Earth of other galaxies

Gravitational field strength, g

The gravitational force exerted per unit mass at a point within a gravitational field

Weight

The gravitational force in an object, measured in newtons, N

Expanding Universe

The idea that the fabric of space and time is expanding in all directions and that as a result any point, in any part of the Universe, is moving away from every other point in the Universe, and the further the points are apart the faster their relative motion away from each other

Supernova

The implosion of a red supergiant at the end of its life, which leads to subsequent ejection of stellar matter into space, leaving an inert remnant core

Resonance

The increase in amplitude of a forced oscillation when the driving frequency matches the natural frequency of the oscillating system

Extension

The increase in length of an object when a tensile force is exerted on it

Gas laws

The laws governing the behaviour of ideal gases, like Boyle's law

Red shift

The lengthening of observed wavelength that occurs when a wave source is moving away from the Earth (receding), the absorption lines in its spectrum will be red-shifted

Boltmann consant

The molar gas constant R divided by the Avogrado contant N_A, a constant that relates the main kinetic energy of atoms or molecules in a gas to the gas temperature- symbol 'k'

Free oscillation

The motion of a mechanical system displaced from its equilibrium position and then allowed to oscillate without any external forces

Free fall

The motion of an object accelerating under gravity with no other force acting on it

Number density

The number of free electrons per cubic metre of a material, symbol 'n', unit m⁻³

Atomic number

The number of protons in a nucleus

Frequency (waves)

The number of wavelengths passing a given point per unit time

Kepler's first law of planetary motion

The orbit of a planet is an ellipse with the sun at one of the two foci

Planetary nebula

The outer layers of a red giant that have drifted off into space, leaving the hot core behind at the centre as a white dwarf

Wien's displacement law

The peak wavelength λ(max) at which the intensity of radiation from a black body is a maximum is inversely proportional to the absolute temperature T of the black body

Polarisation

The phenomenon in which oscillations of a transverse wave are limited to only one plane

Diffraction

The phenomenon in which waves passing through a gap or around an object spread out

Maximum (waves)

The point of greatest amplitude in an interference pattern, produced by constructive interference

Minimum (waves)

The point of least amplitude in an interference pattern, produced by destructive interference

Polycrystalline graphite

Thin layers of graphite with regularly arranged carbon atoms in different orientations

Triangle of forces

Three forces acting at a point in equilibrium, represented by the sides of the triangle

Principle of conservation of momentum

Total momentum of a system remains the same before and after a collision

Newton's third law of motion

When two objects interact, each exerts an equal but opposite force on the other during the interaction

Principle of superposition of waves

When two similar types of waves meet at a point the resultant displacement at that point is equal to the sum of the displacements of the individual waves

Ohm's law

The potential difference across a conductor is directly proportional to the current in the component as long as its temperature remains constant

Terminal p.d.

The potential difference across an electrical power source -- when there is no current this is equal to the e.m.f. minus the lost volts

Lost volts

The potential difference across the internal resistor of a source of e.m.f.

Boyle's law

The pressure of an ideal gas is inversely proportional to its volume, provided that the mass of gas and the temperature do not vary

Decay constant

The probability of decay of an individual nucleus per unit time

Radioactivity

The process by which unstable nuclei split, or decay, emitting ionising radiation (alpha particles, beta particles, and gamma rays)

Time constant

The product of capacitance and resistance, CR, for a capacitor-resistor circuit - equal to the time taken for the p.d. (or the current or the charge) to decrease to e⁻¹ (about 37%) of its initial value when the capacitor discharges through a resistor - symbol τ

Moment

The product of force and perpendicular distance from a pivot or stated point

Work

The product of force and the distance moved in the direction of the force, measured in J

Torque (of a couple)

The product of one of the forces of a couple and the perpendicular distance between the forces

Magnetic flux

The product of the component of the magnetic flux density perpendicular to a given area and that cross-sectional area: φBAcosθ

Acoustic independance

The product of the density 'p' of a substance and the speed 'c' of ultrasound in that substance- symbol Z, SI unit kgm⁻²s⁻¹

Linear momentum

The product of the mass and velocity of a particle, measured in kgms⁻¹ or Ns

Magnetic flux linkage

The product of the number of turns in a coil N and the magnetic flux φ

Piezoelectric effect

The production of an electromotive force (e.m.f.) by some crystals, such as quartz, when they are compressed, stretched, twisted, or distorted

Tension

The pulling force exerted by a string, cable, or chain on an object

Intensity (waves)

The radiant power passing through a surface per unit area -- unit Wm⁻²

Corrected count rate

The radiation count rate measured in an experiment minus the background count rate

Background radiation

The radiation emitted by the surroundings, which must be measured before radiation produced in an experiment can usefully be measured.

Activity

The rate at which nuclei decay or disintegrate in a radioactive source, measures in becquerels (Bq) or decays per second.

Acceleration of free fall

The rate if change of velocity of an object falling in a gravitational field, symbol g

Average speed

The rate of change in distance calculated over a complete journey

Angular velocity

The rate of change of angle for an object moving in a circular path- symbol ω

Newton's second law of motion

The rate of change of momentum of an object is directly proportional to the resultant force and takes place in the direction of the force

Acceleration

The rate of change of velocity, a vector quantity

Electric current

The rate of flow of charge, symbol 'I', measured in ampères, A; normally a flow of electrons in metals ore a flow of ions in electrolytes

Power

The rate of work done, measures in watts, W

Intensity reflection coefficient

The ratio of reflected intensity over incident intensity for ultrasound incident at a boundary

Young modulus

The ratio of tensile stress to tensile strain when these quantities are directly proportional to each other, measured in Pa

Efficiency

The ratio of useful output energy to total input energy, often expressed as a percentage

Hubble's law

The recessional speed 'v' of a galaxy is almost directly proportional to its distance 'd' from the Earth

Total internal reflection

The reflection of all light hitting a boundary between two media back into the original medium when the light is travelling back into the original medium when the light is travelling through the medium with the higher refractive index and the incidence angle at the boundary is greater than the critical angle

Refractive index

The refractive index of a material, n-c/v where 'c' is the speed of light through a vacuum and 'v' is the speed of light through the material

Black hole

The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape it an object would need an escape velocity greater than the speed of light, and therefore nothing, not even photons, can escape

Neutron star

The remnant core of a massive star after the star has gone supernova and (if the mass of the core is greater than the Chandrasekhar limit) the core has collapsed under gravity to an extremely high density (similar to that of an atomic nucleus, ~10¹⁷kgm⁻³), as it is almost entirely made up of neutrons

Pair production

The replacement of a single photon with a particle and a corresponding antiparticle of the same total energy

Internal resistance

The resistance of a source of e.m.f. (e.g. of a cell) due to its construction, which causes a loss in energy/voltage as the charge passes through the source, symbol 'r', SI unit ohm, Ω

Drag force

The resistive force exerted by a fluid on an object moving through it

Equilibrium position (waves)

The resting position of waves or particles in an oscillation

Isotropic

The same in all directions (for example the Universe, appearing the same to any observer regardless of position)

Grating spacing

The separation between adjacent lines or slits in a diffraction grating

Blue shift

The shortening of observed wavelength that occurs when a wave source is moving towards the observer- in astronomy, if a galaxy is moving towards the Earth, the absorption lines in its spectrum will be blue-shifted, that is, moved towards the blue end of the spectrum

Nucleus

The small, positively charged region at the centre of an atom where most of the mass of the atom is concentrated

Instantaneous speed

The speed at the moment it is measured -- speed over an infinitesimal interval of time

Pythagoras' theorum

The square of the length of the hypotenuse of a right-angled triangle equals the sum of the squares of the lengths of the other two sides

Kepler's third law of planetary motion

The square of the orbital period 'T' of a planet is directly proportional to the cube of its average distance 'r' from the Sun

Root mean square speed

The square root of the mean square speed (of all the particles in a gas)

Magnetic flux density

The strength of a magnetic field- defined by the equation F/IL, where 'F' is the force acting on current-carrying conductor placed at right angles to a magnetic field, 'I' is the current in the conductor and 'L' is the length of the conductor in the magnetic field - symbol 'B', unit tesla (T)

Breaking strength

The stress value at the point of fracture, calculated by dividing the breaking force by the cross-sectional area

Internal energy

The sum of randomly distributed kinetic and potential energies of the atoms, ions, or molecules within the substance

Big bang

The theory that at a moment in the past all the matter in the Universe was contained in a singularity (at a single point), the beginning of space and time that expanded rapidly outwards

Compressive deformation

A change in the shape of an object due to compressive forces

Tensile deformation

A change in the shape of an object due to tensile forces

Battery

A collection of cells that transfers chemical energy into electrical emergy

Galaxy

A collection of stars and interstellar dust and gas bound together by their mutual gravitational force

Inelastic collision

A collision in which kinetic energy is transferred to other forms, e.g. heat

Perfectly elastic collision

A collision in which no kinetic energy is transferred

Non-ohmic component

A component that does not obey Ohm's law, e.g. filament lamp and diode

Capacitor

A component that stores charge, consisting of two plates separated by an insulator (dielectric)

Ohmic conductor

A conductor that obeys Ohm's law

Conservation of charge

A conservation law which states that electrical charge can neither be created nor destroyed - the total charge in any interaction must be the same before and after the interaction

Exponential decay

A constant-ratio process in which a quantity decreases by the same factor in equal time intervals

Threshold voltage

The minimum potential difference at which a diode begins to conduct

Electric potential

The work done by an electrical force per unit positive charge to bring a charge from infinity to a point in an electric field - unit Volt or JC⁻¹

Electric potential difference

The work done by an external force per unit positive charge to move a charge between two points in an electric field

Gravitational potential

The work done per unit mass to bring an object from infinity to a point in the gravitational field - unit Jkg⁻¹

Equation of state of an ideal gas

pV=nRT, where n is the number of moles of gas

Homogeneous

Uniform in terms of the distribution of matter across the Universe when viewed on a sufficiently large scale

Magnetic field patterns

Visual representations used in interpreting the direction and strength of magnetic fields

Series circuit

A type of electrical circuit where the components are connected end-to -end

Bacquerel

A unit of activity- one bacquerel is an activity of one decay per second

Derived unit

A unit used to represent a derived quantity, such as N for force

Escape velocity

The minimum velocity at which an object has just enough energy to leave a specified gravitational field

Excited

(an atom) \containing an electron or electrons that have absorbed energy and been boosted into a higher energy level

Impedance matching

(or acoustic matching) The use of two substances with similar acoustic impedance to minimise the reflection of ultrasound at the boundary between them

Acoustic matching

(or impedance matching) The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them.

Frequency

(oscillations) The number of complete oscillation per unit time - unit Hertz, Hz

Nebula

(plural nebulae) A cloud of dust and gas (mainly hydrogen), often many hundreds of times larger than our Solar System

Avogadro constant

6.02x10²³, the number of atoms in 0.012kg (12g) of carbon-12; Symbol N_A

Planetary satellite

A body in orbit around a planet - it may be natural (as a moon) or artificial

Equilibrium

A body is in equilibrium when the net force and net moment acting on it are zero

Satellite

A body orbiting around a planet

Newton's first law of motion

A body will remain at rest or continue to move with constant velocity unless acted upon by a resultant force

Anode

A positively charged electrode

Cation

A positively charged ion, one which is attracted to a cathode

Proton

A positively charged particle, a hadron, found in the nucleus of atoms

Fission

A process in which a large nucleus splits into two smaller nuclei after absorbing a neutron

Fusion

A process in which two smaller nuclei join together to form one larger nucleus

Nuclear fusion

A process in which two smaller nuclei join together to form one larger nucleus

Resistance

A property of a component calculated by dividing the potential difference across it by the current in it, symbol R, unit ohm, Ω

Resistivity

A property of a material, measured in Ωm, defined as the product of the resistance of a component made of the material and its cross-sectional area divided by its length

Quantity

A property of an object, substance, or phenomenon that can be measured

Force

A push or pull on an object, measured in newtons, N

Force constant

A quantity determined by dividing the force by extension (or compression) for an object obeying Hooke's law -- called constant of proportionality, k, in Hooke's law, measured in Nm⁻¹

Derived quantity

A quantity that comes from a combination of base units

Angular frequency

A quantity used in oscillatory motion- equal to the product of frequency 'f' and 2π

Vector quantity

A quantity with magnitude (size) and direction

Scalar quantity

A quantity with magnitude (size) but no direction

Photon

A quantum of electromagnetic energy -- photon energy, E, is given by E=hf, where 'h' is the Planck constant and 'f' is the frequency of the electromagnetic radiation

Electron degeneracy pressure

A quantum-mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle

Radiopharmaceutical

A radioisotope chemically combined with elements that will target particular tissues in order to ensure that the radioisotope reaches the correct organ or tumour for the diagnosis or treatment

Medical tracer

A radiopharmaceutical, that is, a compound labelled with a radioisotope that can be traced inside the body using a gamma camera

Chain reaction

A reaction in which the neutrons from an earlier fission stage are responsible for further fission reactions leading to an exponential growth in the rate of the reactions

Thermal equilibrium

A state in which there is no net flow of thermal energy between the objects involved, that is, objects in thermal equilibrium must be at the same temperature

Plumb-line

A string with a weight used to provide a vertical reference line

Fluid

A substance that can flow, including liquids and gases

Coolant

A substance that removes the thermal energy produced from reactions within a fission reactor

Moderator

A substance used to slow down the fast neutrons produced in fission reactions so that they can propagate the fission reaction

Radial field

A symmetrical field that diminishes with distance² from its centre, such as the gravitational field around a spherical mass or the electron field around a spherical charged object

Spectroscopy

A technique in physics in which spectral lines are identified and measured in order to identify elements present within stars

Stellar parallax

A technique used to determine the distance to stars that are relatively close to the Earth (less than 10pc) by comparing their apparent positions against distant stars 6 months apart

Celsius scale

A temperature scale with 100 degrees between the freezing point and the boiling point of pure water (at atmospheric pressure 1.01x10³ Pa), 0°C and 100°C

Wave-particle duality

A theory that states that matter has both particle and wave properties and also electromagnetic radiation has wave and particulate (photon) nature

Step-down transformer

A transformer with fewer turns on the secondary coil than on the primary coil, and a lower output voltage than input voltage

Step-up transformer

A transformer with more turns on the secondary than on the primary coil, and a higher output voltage than input voltage

Vector triangle

A triangle constructed to scale to determine the resultant of two vectors.

Parallel circuit

A type of branching electrical circuit in which there is more than one path for the current -- components in parallel have the same potential difference

Light-emitting diode

A type of diode that emits light when it conducts electricity

Photomultiplier tube

An apparatus that converts a photon of visible light into an electrical pulse, for example as a part of a gamma camera

Series

An arrangement of electrical components connected end-to-end, that means that the current is the same in each component

Ion

An atom that has either lost or gained electrons and so has a net charge

Resistor

An electrical circuit component that obeys Ohm's law, transferring electrical energy to thermal energy

Potential divider

An electrical circuit designed to divide the potential difference across two or more components (often two resistors) in order to produce a specific output

Filament lamp

An electrical component containing a narrow filament of wire that transfers electrical energy into heat and light

Thermistor

An electrical component that has a resistance that decreases as the temperature increases (a negative temperature coefficient)

Light-dependent resistor

An electrical component with a resistance that decreases as the light intensity incident on it increases

Neutron

An electrically neural particle, a hadron, found in the nucleus of atoms

Free electron

An electron in a metal that is free to move -- sometimes called a delocalised electron

Quark

An elementary particle that can exist in six forms (plus their antiparticles) and joins with other quarks to make up hadrons

Ellipse

An elongated 'circle' with two foci

De Broglie Equation

An equation relating the wavelength and the momentum of a particle λ=h/p or λ=h/mv

Grating equation

An equation that can be used to determine accurately the wavelength of monochromatic light sent through a diffraction grating, dsinθ=nλ

Wave equation

An equation that relates the frequency f in hertz, the wavelength λ in metres and the wave speed v in ms⁻¹: v=fλ

Potential divider equation

An equation with three terminals and some form of sliding contact that can be adjusted to vary the potential difference between two terminals

Red giant

An expanding star at the ends of its life, with an inert core in which fusion no longer takes place, but in which fusion of lighter elements continues in the shell around the core

Ionising radiation

Any form of radiation that can ionise atoms by removing an electron to leave a positive ion

Meson

Any hadron comprising a combination of a quark and an anti-quark

Baryon

Any hadron made with a combination of three quarks

Coulomb's law

Any two point charges exert an electrostatic (electrical) force on each other that is directly proportional to the product of their charges and inversely proportional to the square of their separation

Kirchhoff's first law

At any point in an electrical circuit, the sum of currents into that point is equal to the sum of currents out of that point, electrical charge is conserved

Tensile force

Equal and opposite forces acting on a material to stretch it

Turn-ratio equation

Equation for a transformer: V(s)/V(p)=n(s)/n(p), where output voltage is V(s), input voltage is V(p), the number of turns is the secondary coil is n(s), and number of turns in the primary coil is n(p)

Universe

Everything that exists within space and time

f

Femto, 10⁻¹⁵

Kirchhoff's second law

In a closed loop of an electrical circuit, the sum of currents into that point is equal to the sum of the e.m.f.s is equal to the sum of the p.d.s

Gradient

In a graph, the change in the vertical axis quantity divided by the corresponding change in the horizontal axis quantity

Monochromatic light

Light of a single frequency

Magnetic field lines

Lines of force drawn to represent a magnetic field pattern

Gravitational field lines

Lines of force used to map the gravitational field pattern around an object having mass

Constant velocity

Motion in which the change in the displacement per unit time stays the same

Constant speed

Motion in which the distance travelled per unit time stays the same

Collimator

Part of a gamma camera, a honeycomb of long, thin tubes made from lead that absorbs any photons arriving at an angle to the axis of the tubes so that a clear picture is obtained

Scintillator

Part of a gamma camera, often made of sodium iodide, which produces thousands of photons of visible light when struck by a single gamma photon

Antiphase

Particles oscillating completely out of step with each other (one reaches its maximum positive displacement as the other reaches its maximum negative displacement) are in antiphase

In phase

Particles oscillation perfectly in time with each other (reaching their maximum positive displacement at the same time) are in phase

Out of phase

Particles that are neither in phase, nor antiphase, are out of phase

p

Pico, 10⁻¹²

Voltage

Potential differnece

Radiation pressure

Pressure from the photons in the core of a star, which acts outwards to counteract the pressure from the gravitational force pulling the matter in the star inwards

Ductile

Property of a material that has a large plastic region in a stress-strain graph, so can be drawn into wires

Brittle

Property of a metal that does not show plastic deformation and deforms very little (if at all) under high stress

Oscillating motion

Repetitive motion of an object around its equilibrium position

Interference

Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from two waves

Destructive interference

Superposition of two waves in antiphase so that the waves cancel each other out and the resultant wave has smaller amplitude than the original waves

Constructive interference

Superposition of two waves in phase so that the resultant wave has greater amplitude than the original waves

Planck constant

Symbol 'h', and important constant in quantum mechanics, 6.63x10⁻³⁴Js

SI

Système International d'Unités (International System of Units)

T

Tera, 10¹²

Fundamental frequency

The lowest frequency at which an object (e.g., an air column in a pipe of a string fixed at both ends) can vibrate

Absolute zero

The lowest possible temperature, the temperature at which substances have minimum internal energy

Faraday's law

The magnitude of the induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage

Main sequence

The main period on an H-R diagram in a star's life, during which it is stable

Chandrasekhar limit

The mass of a star's core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse, 1.44 solar masses

Rest mass

The mass of an object, such as a particle, when it is stationary

Molar mass

The mass of one mole of a substance

Density

The mass per unit volume of a substance

Amplitude (waves)

The maximum displacement from the equilibrium position (can be positive or negative)

Trough

The maximum negative amplitude of a transverse wave

Peak

The maximum positive amplitude of a transverse wave

Ultimate tensile strength

The maximum stress that a material can withstand before it breaks

Astronomical unit

The mean distance from the Earth to the Sun, i.e.150 million km or 1.5x10¹¹m

Mean square speed

The mean of the squared velocities (of all the particles in a gas)

Microwave background radiation

The microwave signal of uniform intensity detected from all directions of the sky, which fits the profile for a black body at a temperature of 2.7K

Wavelength

The minimum distance between two points oscillating in phase, for example the distance from one peak to the next or from one compression to the next

Work function

The minimum energy needed to remove a single electron from the surface of a particular metal; symbol φ, measured in J

Binding energy

The minimum energy required to completely separate a nucleus into its constituent protons and neutrons

Threshold frequency

The minimum frequency of electromagnetic radiation that will cause the emission of an electron from the surface of a particular metal - symbol f₀, measured in Hz

Timebase

The time interval represented by one horizontal square on an oscilloscope screen

Time of flight

The time taken for an object to complete its motion

Period (waves)

The time taken for one complete wavelength to pass a given point

Period (oscillations)

The time taken to complete one oscillation

Stopping distance

The total distance travelled from the time when a driver first sees a reason to stop and the time when the vehicle stops, the sum of the thinking distance and the breaking distance

Principle of conservation of energy

The total energy of a closed system remains the constant- energy cannot be created nor can it be destroyed

Nucleon number

The total number of protons and neutrons in a nucleus (also called the mass number); symbol 'A'

Luminosity

The total radiant power output of a star- symbol 'L', unit W

Polarity

The type of charge (positive or negative) or the orientation of a cell relative to a component

Archimedes' principle

The upthrust on an object in a fluid is equal to the weight of fluid it displaces

Upthrust

The upward buoyant force exerted on a body immersed in a fluid

Elastic limit

The value of stress or force beyond which elastic deformation becomes plastic deformation, and the material or object will no longer return to its original shape and size when the stress or force is removed

Limit of proportionality

The value of stress or force beyond which stress is no longer directly proportional to strain

Compressive force

Two or more forces together that reduce the length or volume of an object

Resistor circuit

Two or more resistors arranged to provide a specific resistance

Coherence

Two wave sources, or waves, that are coherent have a constant phase difference

Alpha

Α, α

Beta

Β, β

Gamma

Γ, γ

Delta

Δ, δ

Epsilon

Ε, ε

Zeta

Ζ, ζ

Eta

Η, η

Theta

Θ, θ

Iota

Ι, ι

Kappa

Κ, κ

Lambda

Λ, λ

Mu

Μ, μ

Nu

Ν, ν

Xi

Ξ, ξ

Omnicron

Ο, ο

Pi

Π, π

Rho

Ρ, ρ

Sigma

Σ, σ

Tau

Τ, τ

Upsilon

Υ, υ

Phi

Φ, φ

Chi

Χ, χ

Psi

Ψ, ψ

Omega

Ω, ω


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