IGCSE Physics Glossary
Key definitions, symbols and units from the Cambridge IGCSE Physics 0625 syllabus (2026-2028). Each term includes its exam context and worked examples.
146 terms
A
Absolute Zero
The lowest possible temperature (0 K or -273 degrees Celsius), where particles have minimum kinetic energy.
Acceleration
a (m/s²)
The rate of change of velocity, measured in metres per second squared.
Alpha Particle
α
A particle consisting of two protons and two neutrons, emitted during alpha decay. Identical to a helium-4 nucleus.
Alternating Current (AC)
Definition of alternating current for Cambridge IGCSE Physics 0625, covering how AC differs from DC and where it is used.
Ammeter
An instrument used to measure electric current, connected in series with the component being measured.
Amplitude
A (m)
The maximum displacement of a point on a wave from its rest (equilibrium) position.
Atmospheric Pressure
The pressure exerted by the weight of the air column above a surface, approximately 100 000 Pa at sea level.
B
Background Radiation
Definition of background radiation for Cambridge IGCSE Physics 0625, listing natural and artificial sources and why it must be accounted for in experiments.
Barometer
An instrument used to measure atmospheric pressure, typically using a column of mercury.
Beta Particle
β
A high-speed electron emitted from the nucleus during beta decay, when a neutron converts to a proton.
Boiling Point
The temperature at which a liquid changes to a gas throughout the liquid, with bubble formation, at a given pressure.
Brownian Motion
The random, jerky movement of small visible particles suspended in a fluid, caused by collisions with invisible fluid molecules.
C
Centre of Gravity
The point at which the entire weight of an object can be considered to act.
Centripetal Force
The resultant force directed toward the centre of a circle that keeps an object moving in a circular path.
Circuit Breaker
Definition of a circuit breaker for Cambridge IGCSE Physics 0625, explaining how it protects circuits and its advantages over a fuse.
Compression
A region in a longitudinal wave where particles are pushed closer together.
Conduction (Thermal)
The transfer of thermal energy through a material by particle vibrations and, in metals, by free electron diffusion.
Conservation of Energy
Definition of the principle of conservation of energy for Cambridge IGCSE Physics 0625, with examples of energy transfers and transformations.
Conservation of Momentum
Definition of the principle of conservation of momentum for Cambridge IGCSE Physics 0625, with worked collision and explosion examples.
Convection
The transfer of thermal energy by the movement of a heated fluid (liquid or gas).
Conventional Current
I (A)
The direction of current flow from positive to negative in a circuit, opposite to the direction of electron flow.
Coulomb
C
The SI unit of electric charge. One coulomb is the charge carried by a current of one ampere flowing for one second.
Count Rate
Definition of count rate for Cambridge IGCSE Physics 0625, explaining how it is measured with a Geiger-Muller tube and how to correct for background radiation.
Critical Angle
c (degrees)
The angle of incidence at which the angle of refraction is exactly 90 degrees, beyond which total internal reflection occurs.
Current
I (A)
The rate of flow of electric charge past a point in a circuit, measured in amperes.
D
DC Electric Motor
Definition and working principle of a DC electric motor for Cambridge IGCSE Physics 0625, covering the motor effect, commutator, and how to change speed or direction.
Deceleration
A decrease in speed; acceleration in the opposite direction to the velocity.
Density
ρ (kg/m³)
The mass per unit volume of a substance, showing how compact the matter is.
Diffraction
The spreading of a wave as it passes through a gap or around an obstacle.
Diffusion
Definition of diffusion for Cambridge IGCSE Physics 0625, explaining how particles spread from high to low concentration and the evidence it provides for particle motion.
Diode
A component that allows current to flow in one direction only (forward bias) and blocks it in the other (reverse bias).
Direct Current (DC)
Definition of direct current for Cambridge IGCSE Physics 0625, explaining how DC flows in one direction and its common sources.
Displacement
s (m)
The shortest distance from the starting point to the finishing point, in a stated direction. A vector quantity.
E
Earth Wire
Definition of the earth wire for Cambridge IGCSE Physics 0625, explaining its safety role in three-pin plugs and how it works with a fuse.
Efficiency
The ratio of useful energy output to total energy input, expressed as a decimal or percentage.
Elastic Deformation
Definition of elastic deformation for Cambridge IGCSE Physics 0625, explaining the difference between elastic and plastic behaviour in springs and materials.
Electric Field
A region around a charged object where a force acts on other charged objects.
Electrical Conductor
Definition of electrical conductor for Cambridge IGCSE Physics 0625, explaining how conductors allow current to flow and giving common examples.
Electromagnetic Induction
The generation of an e.m.f. (and current in a complete circuit) when the magnetic flux through a conductor changes.
Electromagnetic Relay
Definition of an electromagnetic relay for Cambridge IGCSE Physics 0625, explaining how a small current controls a separate high-power circuit.
Electromagnetic Spectrum
The continuous range of electromagnetic waves ordered by wavelength or frequency, from radio waves to gamma rays.
Electromotive Force (e.m.f.)
ε (V)
The energy transferred per unit charge by a source of electrical energy, such as a battery or generator.
Electron
e
A subatomic particle with a negative charge and negligible mass, found in orbits around the nucleus.
Energy
E (J)
The capacity to do work, measured in joules. Energy can be transferred between stores but cannot be created or destroyed.
Energy Store
An energy store is a way of describing where energy is held, such as kinetic, gravitational potential, thermal, elastic, chemical or nuclear.
Equilibrium
The state of an object when the resultant force and the resultant moment acting on it are both zero.
Evaporation
The escape of higher-energy molecules from the surface of a liquid at any temperature below its boiling point, causing cooling.
Extension
Extension is the increase in length of a spring or wire when a force is applied, measured in metres.
F
Focal Length
f (m (metres))
Definition of focal length for Cambridge IGCSE Physics 0625, covering converging lenses and how focal length relates to lens power.
Force
F (N)
A push or pull that can change the motion, shape or direction of an object, measured in newtons.
Frequency
f (Hz)
The number of complete waves passing a point per second, or the number of oscillations per second.
Friction
A contact force that opposes the relative motion or attempted motion between two surfaces.
Fuse
A safety device containing a thin wire that melts and breaks the circuit when the current exceeds the rated value.
G
Gamma Ray
γ
High-frequency electromagnetic radiation emitted from an unstable nucleus, with no charge and no mass.
Generator
Definition of an electrical generator for Cambridge IGCSE Physics 0625, explaining how electromagnetic induction produces an alternating current.
Gravitational Field Strength
g (N/kg)
The force per unit mass experienced by an object in a gravitational field, numerically equal to the acceleration due to gravity.
Gravitational Potential Energy
Ep (J)
The energy stored in an object due to its position in a gravitational field.
H
Half-Life
The time taken for the activity of a radioactive sample to halve, or for half the radioactive nuclei to decay.
Hertz
Hz
The SI unit of frequency, equal to one cycle per second.
Hooke's Law
The extension of a spring is directly proportional to the applied force, provided the limit of proportionality is not exceeded.
I
Impulse
The product of force and the time for which it acts, equal to the change in momentum.
Infrared Radiation
Electromagnetic radiation with wavelengths longer than visible red light, associated with thermal energy transfer.
Insulator (Electrical)
A material that does not allow electric charge to flow through it easily, such as plastic, rubber or glass.
Insulator (Thermal)
A material that reduces the rate of thermal energy transfer, such as trapped air, foam or fibreglass.
Internal Energy
Internal energy is the total kinetic energy and potential energy of all the particles in a substance.
Ionisation
Definition of ionisation for Cambridge IGCSE Physics 0625, explaining how radiation removes electrons from atoms and the biological effects of ionising radiation.
Isotope
Atoms of the same element with the same number of protons but different numbers of neutrons.
J
K
Kelvin
K
The SI unit of thermodynamic temperature. 0 K is absolute zero; one kelvin equals one degree Celsius in size.
Kilowatt-Hour (kWh)
kWh (kWh)
Definition of the kilowatt-hour for Cambridge IGCSE Physics 0625, explaining how electricity bills are calculated from power and time.
Kinetic Energy
Ek (J)
The energy stored in a moving object, dependent on its mass and the square of its speed.
L
Latent Heat
The energy absorbed or released during a change of state at constant temperature.
Light-Dependent Resistor (LDR)
Definition of LDR for Cambridge IGCSE Physics 0625, covering how its resistance changes with light intensity and its use in light-sensing circuits.
Light-Emitting Diode (LED)
Definition of LED for Cambridge IGCSE Physics 0625, covering how LEDs work, their advantages over filament lamps, and circuit requirements.
Limit of Proportionality
Definition of the limit of proportionality for Cambridge IGCSE Physics 0625, explaining its position on a force-extension graph and its relationship to Hooke's law.
Live Wire
Definition of the live wire for Cambridge IGCSE Physics 0625, explaining its role in mains circuits and why it is dangerous.
Longitudinal Wave
A wave in which the oscillations are parallel to the direction of energy transfer.
M
Magnetic Field
A region around a magnet or current-carrying conductor where a magnetic force acts on magnetic materials or other magnets.
Magnification
m (no unit (ratio))
Definition of magnification for Cambridge IGCSE Physics 0625, covering the formula and its application to lenses and mirrors.
Manometer
Definition of a manometer for Cambridge IGCSE Physics 0625, explaining how a U-tube manometer measures gas pressure.
Mass
m (kg)
The amount of matter in an object, measured in kilograms. Mass does not change with location.
Melting Point
The temperature at which a solid changes to a liquid at a given pressure.
Moment
The turning effect of a force about a pivot, calculated as force multiplied by perpendicular distance from the pivot.
Moment of a Force
The moment of a force is the turning effect of a force about a pivot, calculated as force multiplied by perpendicular distance.
Momentum
p (kg m/s)
The product of an object's mass and velocity, a vector quantity conserved in collisions and explosions.
N
Neutron
n
A subatomic particle found in the nucleus with no electric charge and a relative mass of 1.
Newton
N
The SI unit of force. One newton is the force that gives a 1 kg mass an acceleration of 1 m/s squared.
Normal Contact Force
The perpendicular force exerted by a surface on an object resting on it, preventing the object from passing through.
Normal Line
The normal is an imaginary line drawn perpendicular to a surface at the point where a ray of light hits it.
Nuclear Fission
The splitting of a large, unstable nucleus into two smaller nuclei, releasing energy and neutrons.
Nuclear Fusion
The joining of two light nuclei to form a heavier nucleus, releasing energy.
Nucleon Number
A
The total number of protons and neutrons in the nucleus of an atom, also called mass number.
O
Ohm
\Omega
The SI unit of electrical resistance. One ohm is the resistance when a potential difference of 1 V drives a current of 1 A.
Ohm's Law
Definition of Ohm's law for Cambridge IGCSE Physics 0625, including the formula, experimental verification, and V-I graph for an ohmic conductor.
Optical Fibre
Definition of optical fibre for Cambridge IGCSE Physics 0625, explaining how total internal reflection keeps light trapped inside the fibre.
Oscillation
A repeated back-and-forth movement about a fixed point, forming the basis of waves and periodic motion.
P
Parallel Circuit
A circuit arrangement where components are connected across the same two points, providing multiple current paths.
Pascal
Pa
The SI unit of pressure, equal to one newton per square metre.
Period
T (s)
The time taken for one complete wave cycle or oscillation to occur.
Potential Difference
V (V)
The energy transferred per unit charge between two points in a circuit, measured in volts.
Power
P (W)
The rate of energy transfer or the rate of doing work, measured in watts.
Pressure
p (Pa)
The force acting per unit area on a surface, measured in pascals.
Principle of Moments
Definition of the principle of moments for Cambridge IGCSE Physics 0625, with worked examples of balanced beams and calculations.
Proton
p
A positively charged subatomic particle found in the nucleus with a relative charge of +1 and a relative mass of 1.
Proton Number
Z
The number of protons in the nucleus of an atom, also called atomic number. It defines the element.
R
Radiation (Thermal)
The transfer of thermal energy by electromagnetic waves, mainly infrared, without requiring a medium.
Radioactive Decay
The spontaneous and random emission of radiation from an unstable nucleus as it becomes more stable.
Rarefaction
A region of lower pressure and lower particle density in a longitudinal wave.
Reflection
The bouncing back of a wave when it meets a boundary between two media.
Refraction
The change in direction of a wave as it passes from one medium to another due to a change in speed.
Refractive Index
The refractive index of a medium is the ratio of the speed of light in a vacuum to the speed of light in the medium.
Renewable Energy
Definition of renewable energy for Cambridge IGCSE Physics 0625, covering types of renewable sources, their advantages and limitations.
Resistance
R (\Omega)
A measure of how much a component opposes the flow of electric current, measured in ohms.
Resultant Force
The single force that has the same effect as all the forces acting on an object combined.
S
Scalar
A quantity that has magnitude only, with no direction.
Series Circuit
A circuit arrangement where components are connected end to end, providing a single path for current.
Snell's Law
The law relating the angles of incidence and refraction to the refractive indices of two media.
Solenoid
Definition of a solenoid for Cambridge IGCSE Physics 0625, explaining the magnetic field pattern inside and outside a current-carrying coil.
Specific Heat Capacity
c (J/(kg °C))
The energy required to raise the temperature of 1 kg of a substance by 1 degree Celsius (or 1 kelvin).
Specific Latent Heat of Fusion
Lf (J/kg)
Definition of specific latent heat of fusion for Cambridge IGCSE Physics 0625, with the formula and explanation of why temperature stays constant during melting.
Specific Latent Heat of Vaporisation
Lv (J/kg)
Definition of specific latent heat of vaporisation for Cambridge IGCSE Physics 0625, with the formula and explanation of the flat section on a heating curve at boiling point.
Speed
v (m/s)
The distance travelled per unit time, a scalar quantity measured in metres per second.
Speed of Light
The speed of light in a vacuum is approximately 3.0 x 10^8 m/s, and is the same for all electromagnetic waves.
Spring Constant
k (N/m)
The force per unit extension of a spring, a measure of stiffness measured in N/m.
States of Matter
Definition of the three states of matter for Cambridge IGCSE Physics 0625, comparing particle arrangement, motion and energy in solids, liquids and gases.
Stopping Distance
Definition of stopping distance for Cambridge IGCSE Physics 0625, covering thinking distance, braking distance, and the factors that affect each.
T
Temperature
A measure of the average kinetic energy of the particles in a substance.
Terminal Velocity
The constant maximum velocity reached when the drag force on a falling object equals its weight.
Thermal Energy
The total kinetic energy of all the particles in a substance, dependent on mass, temperature and specific heat capacity.
Thermistor
A resistor whose resistance changes significantly with temperature, used as a temperature sensor.
Total Internal Reflection
The complete reflection of light at a boundary when the angle of incidence exceeds the critical angle.
Transformer
A device that changes the voltage of an alternating current supply using electromagnetic induction.
Transverse Wave
A wave in which the oscillations are perpendicular to the direction of energy transfer.
U
V
Vector
A quantity that has both magnitude and direction.
Velocity
v (m/s)
The speed of an object in a specified direction, a vector quantity measured in metres per second.
Virtual Image
Definition of virtual image for Cambridge IGCSE Physics 0625, comparing virtual and real images and explaining where each forms.
Visible Light
The part of the electromagnetic spectrum detectable by the human eye, with wavelengths from about 400 to 700 nm.
Volt
V
The SI unit of potential difference and electromotive force. One volt is one joule per coulomb of charge.
Voltmeter
An instrument used to measure the potential difference across a component, connected in parallel.
W
Watt
W
The SI unit of power, equal to one joule per second.
Wave Speed
v (m/s)
The speed at which a wave transfers energy, calculated as frequency multiplied by wavelength.
Wavelength
\lambda (m)
The distance between two consecutive points in phase on a wave, such as crest to crest.
Weight
W (N)
The gravitational force acting on an object, equal to mass multiplied by gravitational field strength.
Work Done
W (J)
The energy transferred when a force moves an object through a distance in the direction of the force.