A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Absolute Zero - (answer)Lowest possible temperature, 0K, object has minimum internal energy.
Acceleration - (answer)Change of velocity per unit time.
Activity of a Radioactive Isotope - (answer)Number of nuclei of the isotope that disintegrate per second.
Becquerel (Bq) - (answer)Unit of radioactive activity, 1Bq = 1 disintegration per second.
Amplitude - (answer)Maximum displacement from equilibrium of oscillating object.
Angular Displacement - (answer)Angle an object in circular motion turns through in radians.
𝜃 = 𝜔t
Angular Speed (ω) - (answer)Rate of change of angular displacement of object in circular motion.
𝜔 = 2𝜋f
Annihilation - (answer)When a *particle and its antiparticle meet*, they destroy each other to *produce
2 photons of equal energy*.
Here the minimum energy of each photon produced = hf(min) = rest energy of the particle.
Antiparticle - (answer)*Equal rest mass* and *equal and opposite charge* to particle.
Atomic Number, Z - (answer)Number of *protons* in nucleus of atom.
Avogadro Constant - (answer)The *number of atoms in 12g of carbon-12*. Used to define the mole.
,A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Back emf - (answer)The emf induced in the spinning coil of electric motor or in any coil in which the
current is changing. A back emf acts against the change of applied pd.
Background Radiation - (answer)*Radiation due to naturally occurring substances* in the environment
e.g. radon gas, cosmic rays, ground and buildings.
Binding Energy - (answer)*Work done* to separate a nucleus into its *constituent nucleons* (neutrons
and protons).
E = mass defect x c²
Binding Energy per Nucleon - (answer)Average work done per nucleon to separate nucleus into
constituent parts. Higher the value, the more stable the nucleus.
*BE per nucleon = BE of a nucleus / mass number*.
Boyle's Law - (answer)For a *fixed mass of gas* at a *constant temperature*, its *pressure x volume is
constant*. Gases that obey this are an ideal gas.
Boltzmann Constant (k) - (answer)Molar gas constant divided by Avogadro number.
Brittle - (answer)Snaps without stretching or bending when subject to stress.
Brownian Motion - (answer)*Random and unpredictable motion of a particle* eg. smoke particles
caused by molecules of the surrounding substance colliding with it. Provided evidence for existence of
atom.
Capacitance - (answer)The *charge stored per unit pd of a capacitor*. Unit is Farad (F) equal to 1
coulomb per volt. Q = CV.
Centre of Mass - (answer)Point through which a single force on the body has no turning effect.
,A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Centripetal Force - (answer)Resultant force on an object that moves along a circular path. Acts towards
centre of circle.
F = mv²/r = m𝜔²r
Chain Reaction - (answer)Series of reactions in which each reaction causes a further reaction e.g. nuclear
fission. Steady reaction where on average one neutron from each fission event goes on to cause a
further fission event.
Charge Carriers - (answer)Charged particles that move through a substance when a pd is applied across
it.
Charles' Law - (answer)For a *fixed mass* of an ideal gas at a *constant pressure*, volume is directly
proportional to its absolute temperature
Coherent - (answer)Two sources of waves emitted with a constant phase difference.
Conservation of Momentum - (answer)Total momentum of objects in system remains constant provided
no external force acts on system.
Control Rods - (answer)Made of *neutron absorbing* materials such as *cadmium* or *boron*. Moved
in and out of reactor core to change rate of fission events to ensure it is *constant*.
Coolant - (answer)Pumped through nuclear reactor core to transfer thermal energy from core to turn
turbine.
Count Rate - (answer)Number of counts per unit time detected by a Geiger-Muller tube. *Corrected by
subtracting background count rate*.
Couple - (answer)Pair of equal and opposite forces acting on a body but not along the same line.
, A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Critical Angle - (answer)Angle of incidence of light ray must exceed the critical angle for total internal
reflection to occur.
sin(Critical Angle) = *n2/n1*, where n1>n2
Critical Mass - (answer)Minimum mas of fissile isotope in a nuclear reactor needed to create a chain
reaction.
Critical Temperature - (answer)Temperature below which a superconductor will have zero resistance.
Cycle - (answer)Interval for a vibrating particle (or wave) from a certain displacement and velocity to the
next time the particle (or wave) has the same displacement and velocity.
Light Damping - (answer)Amplitude of oscillations decreases gradually.
Heavy Damping - (answer)System released and returns to equilibrium without oscillation.
Critical Damping - (answer)System returns to equilibrium in least possible time without oscillating.
de Broglie Wavelength - (answer)Wavelength of matter particle due to wave-particle duality.
Decay Constant - (answer)Probability of an individual nucleus decaying per second.
De-excitation - (answer)Atom loses energy by photon emission as a result of an electron moving from an
outer shell to an inner shell.
Density - (answer)Mass per unit volume.
SOLUTIONS
Absolute Zero - (answer)Lowest possible temperature, 0K, object has minimum internal energy.
Acceleration - (answer)Change of velocity per unit time.
Activity of a Radioactive Isotope - (answer)Number of nuclei of the isotope that disintegrate per second.
Becquerel (Bq) - (answer)Unit of radioactive activity, 1Bq = 1 disintegration per second.
Amplitude - (answer)Maximum displacement from equilibrium of oscillating object.
Angular Displacement - (answer)Angle an object in circular motion turns through in radians.
𝜃 = 𝜔t
Angular Speed (ω) - (answer)Rate of change of angular displacement of object in circular motion.
𝜔 = 2𝜋f
Annihilation - (answer)When a *particle and its antiparticle meet*, they destroy each other to *produce
2 photons of equal energy*.
Here the minimum energy of each photon produced = hf(min) = rest energy of the particle.
Antiparticle - (answer)*Equal rest mass* and *equal and opposite charge* to particle.
Atomic Number, Z - (answer)Number of *protons* in nucleus of atom.
Avogadro Constant - (answer)The *number of atoms in 12g of carbon-12*. Used to define the mole.
,A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Back emf - (answer)The emf induced in the spinning coil of electric motor or in any coil in which the
current is changing. A back emf acts against the change of applied pd.
Background Radiation - (answer)*Radiation due to naturally occurring substances* in the environment
e.g. radon gas, cosmic rays, ground and buildings.
Binding Energy - (answer)*Work done* to separate a nucleus into its *constituent nucleons* (neutrons
and protons).
E = mass defect x c²
Binding Energy per Nucleon - (answer)Average work done per nucleon to separate nucleus into
constituent parts. Higher the value, the more stable the nucleus.
*BE per nucleon = BE of a nucleus / mass number*.
Boyle's Law - (answer)For a *fixed mass of gas* at a *constant temperature*, its *pressure x volume is
constant*. Gases that obey this are an ideal gas.
Boltzmann Constant (k) - (answer)Molar gas constant divided by Avogadro number.
Brittle - (answer)Snaps without stretching or bending when subject to stress.
Brownian Motion - (answer)*Random and unpredictable motion of a particle* eg. smoke particles
caused by molecules of the surrounding substance colliding with it. Provided evidence for existence of
atom.
Capacitance - (answer)The *charge stored per unit pd of a capacitor*. Unit is Farad (F) equal to 1
coulomb per volt. Q = CV.
Centre of Mass - (answer)Point through which a single force on the body has no turning effect.
,A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Centripetal Force - (answer)Resultant force on an object that moves along a circular path. Acts towards
centre of circle.
F = mv²/r = m𝜔²r
Chain Reaction - (answer)Series of reactions in which each reaction causes a further reaction e.g. nuclear
fission. Steady reaction where on average one neutron from each fission event goes on to cause a
further fission event.
Charge Carriers - (answer)Charged particles that move through a substance when a pd is applied across
it.
Charles' Law - (answer)For a *fixed mass* of an ideal gas at a *constant pressure*, volume is directly
proportional to its absolute temperature
Coherent - (answer)Two sources of waves emitted with a constant phase difference.
Conservation of Momentum - (answer)Total momentum of objects in system remains constant provided
no external force acts on system.
Control Rods - (answer)Made of *neutron absorbing* materials such as *cadmium* or *boron*. Moved
in and out of reactor core to change rate of fission events to ensure it is *constant*.
Coolant - (answer)Pumped through nuclear reactor core to transfer thermal energy from core to turn
turbine.
Count Rate - (answer)Number of counts per unit time detected by a Geiger-Muller tube. *Corrected by
subtracting background count rate*.
Couple - (answer)Pair of equal and opposite forces acting on a body but not along the same line.
, A LEVEL PHYSICS AQA DEFINITIONS(LATEST 2025/2026) STUDY GUIDE WITH COMPLETE
SOLUTIONS
Critical Angle - (answer)Angle of incidence of light ray must exceed the critical angle for total internal
reflection to occur.
sin(Critical Angle) = *n2/n1*, where n1>n2
Critical Mass - (answer)Minimum mas of fissile isotope in a nuclear reactor needed to create a chain
reaction.
Critical Temperature - (answer)Temperature below which a superconductor will have zero resistance.
Cycle - (answer)Interval for a vibrating particle (or wave) from a certain displacement and velocity to the
next time the particle (or wave) has the same displacement and velocity.
Light Damping - (answer)Amplitude of oscillations decreases gradually.
Heavy Damping - (answer)System released and returns to equilibrium without oscillation.
Critical Damping - (answer)System returns to equilibrium in least possible time without oscillating.
de Broglie Wavelength - (answer)Wavelength of matter particle due to wave-particle duality.
Decay Constant - (answer)Probability of an individual nucleus decaying per second.
De-excitation - (answer)Atom loses energy by photon emission as a result of an electron moving from an
outer shell to an inner shell.
Density - (answer)Mass per unit volume.
