A LEVEL PHYSICS AQA DEFINITIONS
Absolute Zero - ANS Lowest possible temperature, 0K, object has minimum internal energy.
Acceleration - ANS Change of velocity per unit time.
Activity of a Radioactive Isotope - ANS Number of nuclei of the isotope that disintegrate per
second.
Becquerel (Bq) - ANS Unit of radioactive activity, 1Bq = 1 disintegration per second.
Amplitude - ANS Maximum displacement from equilibrium of oscillating object.
Angular Displacement - ANS Angle an object in circular motion turns through in radians.
𝜃 = 𝜔t
Angular Speed (ω) - ANS Rate of change of angular displacement of object in circular motion.
𝜔 = 2𝜋f
Annihilation - ANS 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 - ANS *Equal rest mass* and *equal and opposite charge* to particle.
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,Atomic Number, Z - ANS Number of *protons* in nucleus of atom.
Avogadro Constant - ANS The *number of atoms in 12g of carbon-12*. Used to define the
mole.
Back emf - ANS 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 - ANS *Radiation due to naturally occurring substances* in the
environment e.g. radon gas, cosmic rays, ground and buildings.
Binding Energy - ANS *Work done* to separate a nucleus into its *constituent nucleons*
(neutrons and protons).
E = mass defect x c²
Binding Energy per Nucleon - ANS 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 - ANS 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) - ANS Molar gas constant divided by Avogadro number.
Brittle - ANS Snaps without stretching or bending when subject to stress.
Brownian Motion - ANS *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.
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,Capacitance - ANS The *charge stored per unit pd of a capacitor*. Unit is Farad (F) equal to 1
coulomb per volt. Q = CV.
Centre of Mass - ANS Point through which a single force on the body has no turning effect.
Centripetal Force - ANS Resultant force on an object that moves along a circular path. Acts
towards centre of circle.
F = mv²/r = m𝜔²r
Chain Reaction - ANS 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 - ANS Charged particles that move through a substance when a pd is applied
across it.
Charles' Law - ANS For a *fixed mass* of an ideal gas at a *constant pressure*, volume is
directly proportional to its absolute temperature
Coherent - ANS Two sources of waves emitted with a constant phase difference.
Conservation of Momentum - ANS Total momentum of objects in system remains constant
provided no external force acts on system.
Control Rods - ANS 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*.
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, Coolant - ANS Pumped through nuclear reactor core to transfer thermal energy from core to
turn turbine.
Count Rate - ANS Number of counts per unit time detected by a Geiger-Muller tube.
*Corrected by subtracting background count rate*.
Couple - ANS Pair of equal and opposite forces acting on a body but not along the same line.
Critical Angle - ANS 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 - ANS Minimum mas of fissile isotope in a nuclear reactor needed to create a
chain reaction.
Critical Temperature - ANS Temperature below which a superconductor will have zero
resistance.
Cycle - ANS 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 - ANS Amplitude of oscillations decreases gradually.
Heavy Damping - ANS System released and returns to equilibrium without oscillation.
Critical Damping - ANS System returns to equilibrium in least possible time without
oscillating.
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Absolute Zero - ANS Lowest possible temperature, 0K, object has minimum internal energy.
Acceleration - ANS Change of velocity per unit time.
Activity of a Radioactive Isotope - ANS Number of nuclei of the isotope that disintegrate per
second.
Becquerel (Bq) - ANS Unit of radioactive activity, 1Bq = 1 disintegration per second.
Amplitude - ANS Maximum displacement from equilibrium of oscillating object.
Angular Displacement - ANS Angle an object in circular motion turns through in radians.
𝜃 = 𝜔t
Angular Speed (ω) - ANS Rate of change of angular displacement of object in circular motion.
𝜔 = 2𝜋f
Annihilation - ANS 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 - ANS *Equal rest mass* and *equal and opposite charge* to particle.
Copyright ©2025 BRIGHTSTARS ALL RIGHTS RESERVED 1
,Atomic Number, Z - ANS Number of *protons* in nucleus of atom.
Avogadro Constant - ANS The *number of atoms in 12g of carbon-12*. Used to define the
mole.
Back emf - ANS 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 - ANS *Radiation due to naturally occurring substances* in the
environment e.g. radon gas, cosmic rays, ground and buildings.
Binding Energy - ANS *Work done* to separate a nucleus into its *constituent nucleons*
(neutrons and protons).
E = mass defect x c²
Binding Energy per Nucleon - ANS 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 - ANS 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) - ANS Molar gas constant divided by Avogadro number.
Brittle - ANS Snaps without stretching or bending when subject to stress.
Brownian Motion - ANS *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.
Copyright ©2025 BRIGHTSTARS ALL RIGHTS RESERVED 2
,Capacitance - ANS The *charge stored per unit pd of a capacitor*. Unit is Farad (F) equal to 1
coulomb per volt. Q = CV.
Centre of Mass - ANS Point through which a single force on the body has no turning effect.
Centripetal Force - ANS Resultant force on an object that moves along a circular path. Acts
towards centre of circle.
F = mv²/r = m𝜔²r
Chain Reaction - ANS 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 - ANS Charged particles that move through a substance when a pd is applied
across it.
Charles' Law - ANS For a *fixed mass* of an ideal gas at a *constant pressure*, volume is
directly proportional to its absolute temperature
Coherent - ANS Two sources of waves emitted with a constant phase difference.
Conservation of Momentum - ANS Total momentum of objects in system remains constant
provided no external force acts on system.
Control Rods - ANS 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*.
Copyright ©2025 BRIGHTSTARS ALL RIGHTS RESERVED 3
, Coolant - ANS Pumped through nuclear reactor core to transfer thermal energy from core to
turn turbine.
Count Rate - ANS Number of counts per unit time detected by a Geiger-Muller tube.
*Corrected by subtracting background count rate*.
Couple - ANS Pair of equal and opposite forces acting on a body but not along the same line.
Critical Angle - ANS 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 - ANS Minimum mas of fissile isotope in a nuclear reactor needed to create a
chain reaction.
Critical Temperature - ANS Temperature below which a superconductor will have zero
resistance.
Cycle - ANS 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 - ANS Amplitude of oscillations decreases gradually.
Heavy Damping - ANS System released and returns to equilibrium without oscillation.
Critical Damping - ANS System returns to equilibrium in least possible time without
oscillating.
Copyright ©2025 BRIGHTSTARS ALL RIGHTS RESERVED 4
