Physics
Cambridge IGCSE
Cambridge IGCSE
Note: This glossary is intended to aid students studying GCSE physics by explaining physics terms.
It is not intended to offer strict concise definitions.
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A B C D E F G H I K L M N O P R S T U V W
| A | |
| absolute magnitude | A measure of the brightness of a star when viewed from a standard distance away. |
| acceleration | The rate of change of velocity. (When a body 'speeds up'). |
| alpha particles/radiation | Nuclear radiation consisting of 2 protons and 2 neutrons. |
| alternating current | Current that continuously changes direction. |
| ammeter | Used to measure current in circuits. |
| amplitude | The height of a wave from the centre line. |
B |
|
| background radiation | Radiation that is all around us, caused by natural sources and man-made sources. |
| balanced (forces) | Forces that cancel out to leave no resultant force. |
| battery | Two or more cells joined together. |
| beta particles/radiation | Nuclear radiation consisting of fast moving electrons. |
| big bang theory | The idea that the universe had a beginning. It was formed approximately 14 billion years ago. |
| black hole | A star that has collapsed down into a point, but retaining a very strong gravitational field. |
| braking distance | The distance travelled by a vehicle whilst the brakes are applied. |
C |
|
| carbon dating | The use of the isotope carbon-14 to find the age of a sample. |
| chain reaction | A self sustaining nuclear reaction. |
| circuit breaker | A device that automatically stops current flowing in a circuit if faults are detected. |
| commutator | A device used to switch the current flow in the coil of a motor or generator. |
| conservation of momentum | The total momentum before and after a collision remains the same, unless external forces are applied. |
| contamination (of radioactivity) | A radioactive isotope is present within an object. |
| control rods | Rods that absorb neutrons in a nuclear fission reaction, to slow it down. |
| convection | The transfer of heat by a moving fluid. (for example - hot air rising). |
| conventional current | Current in a circuit defined as flowing from positive to negative. |
| cosmic microwave background | Left over microwave radiation from the big bang. Found throughout the universe. |
| critical angle | The smallest angle of incidence where light is reflected internally at a boundary, instead of being refracted. |
D |
|
| density | The mass per unit volume of a substance. Measured in kg/m3 or g/cm3. |
| diodes | Electrical devices that only allow current to flow in one direction. |
| direct current | Current that flows in one direction only, at a constant value. |
| displacement | The distance travelled in a specific direction. (A 'vector' quantity). |
| dissipated energy | Energy lost to the environment. |
| doppler effect | The change in frequency caused by relative movement between source and observer. |
E |
|
| elastic behavior | Found when an elastic material can be stretched and then will return to its original length or shape |
| elastic energy | Energy stored by stretching (or compressing) an elastic material |
| electromagnetic spectrum | The family of electromagnetic waves of varying frequencies, such as light and radio waves. |
| electrostatic energy | Energy stored by the attraction or repulsion between charged objects. |
| energy conservation | The idea that energy cannot be created or destroyed, only converted from one form or store to another. |
F |
|
| fission (nuclear) | The process of releasing energy by splitting atoms (e.g. uranium). |
| fluorescence | Found when a substance absorbs ultraviolet light and re-emits visible light. |
| fossil fuels | Fuels formed over millions of years from fossilized plants and animals |
| free fall | When a body falls freely under gravity. |
| frequency | The number of waves per second (measured in hertz, Hz) |
| fuses | Thin wire that melts and breaks a circuit when the current is too high |
| fusion (nuclear) | The process of releasing energy by atoms fusing (joining) together (e.g. hydrogen in stars). |
G |
|
| galaxy | A group of billions of stars. |
| geothermal power | Power produced from heat from hot rocks and volcanic activity underground. |
| gravitational potential energy | Energy stored by an object raised upwards. |
| gravitational field strength, 'g' | The force of gravity pulling downwards per kilogram. (On Earth, g = 9.8 N/kg) |
H |
|
| half-life | The time taken for half of the particles in a radioactive sample to decay. Is is also the time taken for the activity to halve. |
| Hooke's Law | The idea that for some elastic materials, the extension is proportional to the force applied. |
| Hubble's Law | The universe is expanding, such that the 'recession' (moving away) velocity of galaxies is proportional to the distance from the Earth. |
I |
|
| induction | The production of a voltage in a conductor by movement relative to a magnetic field. |
| insulation | Materials such as wool used to prevent heat loss - poor heat conductors. |
| ionising radiation | Nuclear radiation that can affect atoms by 'knocking' an electron out of orbit. |
| irradiation | When a substance is exposed to nuclear radiation. |
| isotopes | Two nuclear isotope atoms will have the same number of protons but a different number of neutrons. |
K |
|
| kinetic energy | Energy stored in a moving object. |
L |
|
| LDRs | Light dependent resistors, that typically have a lower resistance when the light level increases. |
| LEDs | Light emitting diodes. |
| limit of proportionality | The point where an elastic substance no longer follows Hooke's law and the extension is not proportional to the force applied. |
| longitudinal waves | Waves where the particle movement (or 'oscillation') is in the same direction as the wave motion. |
M |
|
| main sequence stars | Stars that are in their main hydrogen burning phase, and are stable. This is the middle phase in the life-cycle of a star. |
| mains electricity | Electricity that is found in homes and offices, typically alternating current of 240V. |
| mass | A measure of the amount of matter present in an object. It is measured in kilograms (kg). |
| medical tracers | A radioactive isotope that is injected into a patient, and can be used to trace where it travels to by the radiation emitted. |
| moderator (nuclear) | A substance used in a nuclear fission reactor to slow down neutrons to a suitable speed for fission to occur. |
| moment | A 'turning force' - calculated by finding the force x the perpendicular distance to the pivot of the rotating system. |
| momentum | A measure of how difficult it is to stop a body from moving. It is defined as the mass x the velocity of a moving object. |
| motor effect | The effect of producing a force on a wire by passing a current through it whilst in a magnetic field. |
| motors | A device for turning electrical energy into rotational kinetic energy. |
N |
|
| national grid | A network of high voltage cables all around a country providing electrical energy to all. |
| nebula | An enormous cloud of gas and dust in space. |
| neutron star | An extremely dense star where electrons and protons have been forced together under very strong gravity to produce a star made entirely of neutrons. |
| Newton's third law | 'Action and reaction are equal and opposite'. (If object A pushes on B, then B pushes back on A with an equal but opposite force). |
| normal line | A line drawn perpendicular to a mirror or surface to allow angles of incidence/reflection/refraction to be measured. |
| nuclear waste | The dangerous radioactive isotopes left as a result of fission in a nuclear power station. |
O |
|
| optical fibres | Thin glass wires that allow light to be transmitted along them by total internal reflection. |
| orbits | One object travelling around another in space. |
| oscilloscope | A device for displaying waves on a screen. |
P |
|
| period | Also called the time period - the time taken for one complete wave or oscillation. |
| pitch | A description of frequency. High pitched = high frequency. |
| pivot | The centre of rotation of a system. |
| potential difference | The voltage across a component or section of a circuit. |
| potential energy | See gravitational potential energy. |
| power | The work done per second. Measured in watts (W). |
| pressure | The force acting on a unit area. Measured in pascals (Pa) or N/cm2 |
| prism | A glass or plastic triangular block used to refract light. |
R |
|
| radioactivity | A substance is radioactive if the atoms are unstable and decay by emitting particles or rays. |
| radiotherapy | Nuclear radiation used to kill cancer cells. |
| red giant | A star that runs out of hydrogen in its core and swells up into a large but cooler red star. |
| red shift | The lengthening of the wavelength of light emitted from galaxies travelling at high speeds away from us. Evidence for an expanding universe. |
| refraction | The bending of light by glass/water/plastic or similar substance. |
| resistance | A high resistance in a circuit means there will be a low current flowing. Resistance is measured in ohms (Ω). |
| resultant (force) | The result of adding two or more forces together. |
| right-hand grip rule | used to predict the magnetic field direction around a current-carrying conductor. |
S |
|
| scalar | A measurement with size but no direction. (measurements that are not vectors). |
| solar system | A star with planets (or sometimes other stars) in orbit around it. |
| solenoid | A coil of wire used as an electromagnet. |
| specific heat capacity | The energy needed to heat 1 kg by 10C. Different substances have different S.H.C.'s, measured in J/kg/0C |
| speed | The distance travelled per unit time, typically measured in m/s or km/h. |
| stars | A large body in space that gives out heat and light through nuclear fusion reactions. |
| states of matter | A phrase used to describe solids, liquids and gases. |
| static electricity | Electricity produced by friction between surfaces. It typically collects on a surface and remains there. |
| stopping distance | The total distance required to stop a vehicle. It is equal to the thinking distance + the braking distance. |
| supernova | A giant explosion caused when a huge star runs out of nuclear fuel in the core. |
T |
|
| terminal velocity | The top speed of an object, reached when friction/air resistance balances the driving force. |
| thermal conductivity | A measure of how easily heat conducts through a material. Metals have a high thermal conductivity. |
| thermal energy | Energy stored as heat. |
| thermistors | A resistor that changes value as the temperature changes. (Typically, they have lower resistance at high temperatures). |
| thinking distance | The time taken by a driver of a vehicle to react before applying the brake. |
| tidal power | Power produced by the movement of the sea caused by tides. |
| time period (wave) | See period. |
| total internal reflection (TIR) | Happens when light is reflected from the inside surface of a material. Only occurs above the critical angle. |
| transformers | A device used to increase or decrease the voltage. Only works with a.c. |
| transverse waves | Waves where the particle movement (or 'oscillation') is in the same direction as the wave motion. |
U |
|
| unbalanced (forces) | Forces that - when added together - do not cancel each other out and leave a resultant force. |
V |
|
| vector | A measurement with size and direction. |
| velocity | The speed of an object in a particular direction. Velocity is a vector measurement. |
| voltage | The 'kick' or 'push' that makes a current flow in a circuit. |
W |
|
| wasted energy | Energy lost (often as heat) when a device tries to convert energy from one form to another. |
| wavefront | An imaginary line joining neighbouring peaks on a wave. (Surfers ride 'wavefronts' towards the shore). |
| weight | The pull of gravity on an object. It is a force so is measured in newtons (N). |
| white dwarf | A small, white hot star that has collapsed and run out of fuel for fusion. It is the end stage of typical stars like the Sun. |
| work | Work is done when energy is transferred from one store or form to another. |
