Black body radiation 

The radiation emitted by a perfect black body (a body that absorbs all the radiation that hits it) 

Infrared radiation 

Electromagnetic waves between visible light and microwaves in the electromagnetic spectrum 

Specific

heat capacity: 

 Energy needed to raise the temperature of 1 kg of a substance by 1 °C 

Thermal conductivity: 

 Property of a material that determines the energy transfer through it by conduction 

Biofuel 

Any fuel taken from living or recently living materials, such as animal waste 

Carbon-neutral: 

A biofuel from a living organism that takes in as much carbon dioxide from the atmosphere as is released when the fuel is  burned 

Geothermal energy: 

 Energy released by radioactive substances deep within the Earth.

National grid 

The network of cables and transformers used to transfer electricity from power stations to consumers (i.e., homes, shops, offices, factories etc.) 

Nuclear fuel 

Substance used in nuclear reactors that releases energy due to nuclear fission 

Nucleus 

Tiny positively charged object composed of protons and neutrons at the centre of every atom 

Reactor core 

The thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor 

Renewable energy: 

Energy from natural sources that is always being replenished so it never runs out 

Diode 

A non-ohmic conductor that has a much higher resistance in one direction (its reverse direction) than in the other direction (its forward direction) 

Electric field 

A charged object (X) creates an electric field around itself, which causes a non-contact force on any other charged object in the field 

Electrons 

Tiny negatively charged particles that move around the nucleus of an atom 

Ion 

A charged atom or molecule 

LDR

A resistor whose resistance depends on the intensity of the light incident on it 

light-emitting diode (LED) 

a diode that emits light when it conducts 

line of force in an electric field 

line along which a free positive charge moves long in an electric field 

neutrons 

uncharged particles of the same mass as protons. The nucleus of an atom consists of protons and neutrons 

Ohm’s law 

the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor 

parallel 

components connected in a circuit so that the potential difference is the same across each one 

potential difference 

a measure of the work done, or energy transferred to the lamp by each coulomb of charge that passes through it. The unit of potential difference is the volt (V) 

protons 

positively charged particles with an equal and opposite charge to that of an electron 

resistance 

resistance (in ohms, Ω) = potential difference (in volts, V) ÷ current (in amperes, A) 

series 

components connected in a circuit in such a way that the same current passes through them 

static electricity 

electric charge stored on insulated objects 

thermistor 

a resistor whose resistance depends on the temperature of the thermistor 

alternating current (a.c.) 

electric current in a circuit that repeatedly reverses its direction 

direct current (d.c.) 

electric current in a circuit that is in one direction only 

earth wire 

the wire in a mains cable used to connect the metal case of an appliance to earth 

fuse 

a fuse contains a thin wire that melts and cuts the current off if too much current passes through it 

live wire 

the mains wire that has a voltage that alternates in voltage (between +325 V and -325 V in Europe) 

neutral wire 

the wire of a mains circuit that is earthed at the local substation so its potential is close to zero 

oscilloscope 

a device used to display the shape of an electrical wave 

plugs 

a plug has an insulates case and is used to connect the cable from an appliance to a socket 

step-down transformers 

electrical device used to step-down the size of an alternating potential difference 

step-up transformers 

electrical device used to step-up the size of an alternating potential difference 

three-pin plug 

a three-pin plug has a live pin, a neutral pin and an earth pin 

boiling point 

temperature at which a pure substance boils or condenses 

Boyle’s Law 

for a fixed mass of gas at constant temperature, its pressure multiplied by its volume is constant 

density 

mass per unit volume of a substance 

freezing point 

the temperature at which a pure substance freezes 

internal energy 

the energy of the particles of a substance due to their individual motion and positions 

latent heat 

the energy transferred to or from a substance when it changes its state 

melting point 

temperature at which a pure substance melts or freezes (solidifies) 

physical change 

a change in which no new substances are produced 

pressure 

force per unit cross-sectional area for a force acting on a surface at right angles to the surface. The unit of pressure is the pascal (Pa) or newton per square metre (N/m2) 

specific latent heat of fusion Lf 

energy needed to melt 1 kg of a substance with no change of temperature 

specific latent heat of vaporisation Lv 

energy needed to boil away 1 kg of a substance with no change of temperature 

boiling point 

temperature at which a pure substance boils or condenses 

Boyle’s Law 

for a fixed mass of gas at constant temperature, its pressure multiplied by its volume is constant 

density 

mass per unit volume of a substance 

freezing point 

the temperature at which a pure substance freezes 

internal energy 

the energy of the particles of a substance due to their individual motion and positions 

latent heat 

the energy transferred to or from a substance when it changes its state 

melting point 

temperature at which a pure substance melts or freezes (solidifies) 

physical change 

a change in which no new substances are produced 

pressure 

force per unit cross-sectional area for a force acting on a surface at right angles to the surface. The unit of pressure is the pascal (Pa) or newton per square metre (N/m2) 

specific latent heat of fusion Lf 

energy needed to melt 1 kg of a substance with no change of temperature 

specific latent heat of vaporisation Lv 

energy needed to boil away 1 kg of a substance with no change of temperature 

activity 

the number of unstable atoms that decay per second in a radioactive source 

alpha radiation (α) 

alpha particles, each composed of two protons and two neutrons, emitted by unstable nuclei 

atomic number  

the number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number 

beta radiation (β) 

beta particles that are high energy electrons created in, and emitted from, unstable nuclei 

chain reaction 

reactions in which one reaction causes further reactions, which in turn cause further reactions, etc. 

count rate 

the number of counts per second detected by a Geiger counter 

gamma radiation (γ) 

electromagnetic radiation emitted from unstable nuclei in radioactive substances 

half-life 

average time taken for the number of nuclei of the isotope (or mass of the isotope) in a sample to halve 

ionisation 

irradiated 

any process in which atoms become charged 

an object that has been exposed to ionising radiation 

isotopes 

atoms with the same number of protons and different numbers of neutrons 

mass number 

the number of proton and neutrons in a nucleus 

moderator 

substance in a nuclear reactor that slows down fission neutrons 

nuclear fission 

the process in which certain nuclei (uranium-235 and plutonium-239) split into two fragments, releasing energy and two or three neutrons as a result 

nuclear fission reactor 

reactors that release energy steadily due to the fission of a suitable isotope, such as uranium-235 

nuclear fusion 

the process where small nuclei are forced together to fuse and form a larger nucleus 

radioactive contamination 

the unwanted presence of materials containing radioactive atoms on other materials 

reactor core 

the thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor 

displacement 

distance in a given direction 

driving force 

force of a vehicle that makes it move (sometimes referred to as motive force) 

effort 

the force applied to a device used to raise a weight or move an object 

force multiplier 

a lever used so that a weight or force can be moved by a smaller force 

forces 

a force (in newtons, N) can change the motion of an object 

free-body force diagram 

a diagram that shows the forces acting on an object without any other objects or forces shown 

friction 

the force opposing the relative motion of two solid surfaces in contact 

load 

the weight of an object raised by a device used to lift the object, or the force applied by a device when it is used to shift an object 

magnitude 

the size or amount of a physical quantity 

moment 

the turning effect of a force defined by the equation: moment of a force (in newton metres, Nm) = force (in newtons, N) x perpendicular distance from the pivot to the line of action of the force (in metres, m) 

Newton’s first law of motion 

if the resultant force on an object is zero, the object stays at rest if it is stationary, or it keeps moving with the same speed in the same direction 

Newton’s third law of motion 

when two objects interact with each other, they exert equal and opposite forces on each other 

parallelogram of forces 

a geometrical method used to find the resultant of two forces that do not act along the same line 

principle of moments 

for an object in equilibrium, the sum of all the clockwise moments about any point = the sum of all the anti-clockwise moments about that point 

resultant force 

a single force that has the same effect as all the forces acting on the object 

scalar 

a physical quantity, such as mass or energy, that has magnitude only (unlike a vector which has magnitude and direction) 

vector 

a vector is a physical quantity, such as displacement or velocity, that has a magnitude and a direction (unlike a scalar which has magnitude only) 

acceleration 

change of velocity per second (in metres per second per second, m/s2) 

deceleration 

change of velocity per second when an object slows down 

displacement 

distance in a given direction 

gradient (of a straight line graph) 

change of the quantity plotted on the y-axis divided by the change of the quantity plotted on the x-axis 

tangent 

a straight line drawn to touch a point on a curve so it has the same gradient as the curve at that point 

velocity 

speed in a given direction (in metres/second, m/s) 

braking distance 

the distance travelled by a vehicle during the time it takes for its brakes to act 

conservation of momentum 

in a closed system, the total momentum before an event is equal to the total momentum after the event. Momentum is conserved in any collision or explosion, provided no external forces act on the objects that collide or explode 

directly proportional 

a graph will show this if the line of best fit is a straight line through the origin 

elastic 

a material is elastic if it is able to regain its shape after it has been squashed or stretched 

extension 

the increase in length of a spring (or a strip of material) from its original length 

gravitational field strength, g 

the force of gravity on an object of mass 1 kg (in newtons per kilogram, N/kg). It is also the acceleration of free fall 

inertia 

the tendency of an object to stay at rest or to continue in uniform motion 

limit of proportionality 

the limit for Hooke’s law applied to the extension of a stretched spring 

mass 

the quantity of matter in an object – a measure of the difficulty of changing the motion of an object (in kilograms, kg) 

momentum 

this equals mass (in kg) x velocity (in m/s) 

Newton’s second law of motion 

the acceleration of an object is proportional to the resultant force on the object, and inversely proportional to the mass of the object 

stopping distance 

the distance travelled by the vehicle in the time it takes for the driver to think and brake 

terminal velocity 

the velocity reached by an object when the drag force on it is equal and opposite to the force making it move 

thinking distance 

the distance travelled by the vehicle in the time it takes the driver to react 

weight 

the force of gravity on an object (in newtons, N) 

upthrust 

the upward force that acts on a body partly or completely submerged in a fluid 

amplitude 

the height of a wave crest or trough of a transverse wave from the rest position. For oscillating motion, the amplitude is the maximum distance moved by an oscillating object from its equilibrium position 

compression 

squeezing together 

echo 

reflection of sound that can be heard 

electromagnetic waves 

electric and magnetic disturbances that transfer energy from one place to another 

frequency 

the number of wave crests passing a fixed point every second 

longitudinal waves 

waves in which the vibrations are parallel to the direction of energy transfer 

mechanical wave 

vibration that travels through a substance 

oscillate 

move to and fro about a certain position along a line 

primary seismic wave (P-wave) 

longitudinal waves that push or pull on the material that they move through as they travel through the Earth 

rarefaction 

stretched apart 

reflection 

the change of direction of a light ray or wave at a boundary when the ray or wave stays in the incident medium 

refraction 

the change of direction of a light ray when it passes across a boundary between two transparent substances (including air) 

secondary seismic wave (S-wave) 

transverse waves that shake the Earth side to side as they pass through 

seismic waves 

sound wave at frequency greater than 20 000 Hz (the upper frequency limit of the human ear) 

speed 

the speed of an object (metres per second) = distance moved by the object (metres) ÷ time taken to move the distance travelled (seconds) 

transmission/transmitted 

a wave passing through a substance 

transverse wave 

a wave where the vibration is perpendicular to the direction of energy transfer 

ultrasound wave 

sound wave at frequency greater than 20 000 Hz (the upper frequency limit of the human ear) 

vibrate 

oscillate (move to and fro) rapidly about a certain position 

wavelength 

the distance from one wave crest to the next 

carrier waves 

waves used to carry any type of signal 

charge-coupled device (CCD) 

an electronic device that creates an electronic signal from an optical image formed on the CCD’s array of pixels 

contrast medium 

an X-ray absorbing substance used to fill a body organ so the organ can be seen on a radiograph 

electromagnetic spectrum 

the continuous spectrum of electromagnetic waves 

ionisation 

any process in which atoms become charged 

microwaves 

electromagnetic waves between infrared radiation and radio waves in the electromagnetic spectrum 

optical fibre 

thin glass fibre used to transmit light signals 

radiation dose 

amount of ionising radiation a person receives 

radio waves 

electromagnetic waves of wavelengths greater than 0.10m 

ultraviolet radiation (UV) 

electromagnetic waves between visible light and X-rays in the electromagnetic spectrum 

wave speed 

the distance travelled per second by a wave crest or trough 

white light 

light that includes all the colours of the spectrum 

angle of incidence 

angle between the incident ray and the normal 

angle of reflection 

angle between the reflected ray and the normal 

concave (diverging) lens 

a lens that makes parallel rays diverge (spread out) 

convex (converging) lens 

a lens that makes light rays parallel to the principal axis converge (meet) at a point 

diffuse reflection 

reflection from a rough surface - the light rays are scattered in different directions 

focal length 

the distance from the centre of a lens to the point where light rays parallel to the principal axis are focused (or, in the case of a diverging lens, appear to diverge from) 

magnification 

the image height ÷ the object height 

magnifying glass 

a converging lens used to magnify a small object which must be placed between the lens and its focal point 

normal 

straight line through a surface or boundary perpendicular to the surface or boundary 

opaque object 

an object that light cannot pass through 

principal focus 

the point where light rays parallel to the principal axis of a lens are focused (or, in the case of a diverging lens, appear to diverge from) 

real image 

an image formed by a lens that can be projected on a screen 

refraction 

the change of direction of a light ray when it passes across a boundary between two transparent substances (including air) 

specular reflection 

reflection from a smooth surface. Each light ray is reflected in a single direction 

translucent object 

an object that allows light to pass through, but the light is scattered or refracted 

transparent object 

an object that transmits all the incident light that enters the object 

virtual image 

an image, seen in a lens or a mirror, from which light rays appear to come after being refracted by a lens or reflected by a mirror 

alternator 

an alternating current generator 

dynamo 

a direct-current generator 

electromagnet 

an insulated wire wrapped round an iron bar that becomes magnetic when there is a current in the wire 

electromagnetic induction 

the process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of force of a magnetic field 

Fleming’s left-hand rule 

a rule that gives the direction of the force on a current-carrying wire in a magnetic field according to the directions of the current and the field 

generator effect 

the production of a potential difference using a magnetic field 

induced magnetism 

magnetism of an unmagnetised magnetic material by placing it in a magnetic field 

magnetic field 

the space around a magnet or a current-carrying wire 

magnetic field line 

line in a magnetic field along which a magnetic compass points – also called a line of force 

magnetic flux density 

a measure of the strength of the magnetic field defined in terms of the force on a current-carrying conductor at right angles to the field lines  

motor effect 

when a current is passed along a wire in a magnetic field, and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field 

solenoid 

a long coil of wire that produces a magnetic field in and around the coil when there is a current in the coil 

split-ring commutator 

metal contacts on the coil of a direct current motor that connects the rotating coil continuously to its electric power supply 

step-down transformer 

electrical device that is used to step-down the size of an alternating potential difference 

step-up transformer 

electrical device that is used to step-up the size of an alternating potential difference 

transformer 

electrical device used to change an (alternating) voltage. See also step-up transformer and step-down transformer 

Big Bang theory 

the theory that the universe was created in a massive explosion (the Big Bang), and that the universe has been expanding ever since 

black dwarf 

a star that has faded out and gone cold 

black hole 

an object in space that has so much mass that nothing, not even light, can escape from its gravitational field 

centripetal force 

the resultant force towards the centre of a circle acting on an object moving in a circular path 

cosmic microwave background radiation (CMBR) 

electromagnetic radiation that has been travelling through space ever since it was created shortly after the Big Bang 

dark matter 

matter in a galaxy that cannot be seen. Its presence is deduced because galaxies would spin much faster if their stars were their only matter 

main sequence 

the main sequence is the life stage of a star during which it radiates energy because of fusion of hydrogen nuclei in its core 

neutron star 

the highly compressed core of a massive star that remains after a supernova explosion 

protostar 

the concentration of dust clouds and gas in space that forms a star 

red giant 

a star that has expanded and cooled, resulting in it becoming red and much larger and cooler than it was before it expanded 

red supergiant 

a star much more massive than the Sun will swell out after the main sequence stage to become a red supergiant before it collapses 

red-shift 

increase in the wavelength of electromagnetic waves emitted by a star or galaxy due to its motion away from us. The faster the speed of the star or galaxy, the greater the red-shift is 

supernova 

the explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses on to the core and rebounds 

white dwarf 

a star that has collapsed from the red giant stage to become much hotter and denser