Physics A-Level Dictionary

Absolute zeroThe lowest possible temperature at which a gas would have a zero volume.
Absorption spectrumThe spectrum of electromagnetic radiation absorbed by matter when radiation of all frequencies is passed through it.
ActivityThe number of decays per second of a radioactive substance.
AntinodeThe point of maximum displacement of a stationary wave.
Binding energyThe negative of the amount of energy needed to separate a nucleus into individual nucleons.
BosonThe carrier particle that mediates the weak nuclear force.
CapacitanceThe ratio of charge stored per increase in potential difference.
CapacitorAn electrical device used to store charge and energy in the electrical field.
Circular motionMotion with constant radius of curvature caused by a centripetal force and acceleration that is perpendicular to velocity.
Coherent wavesWaves that have a constant phase difference.
De Broglie wavelengthLength of de Broglie wave of a particle, equal to Planck’s constant divided by the momentum of the particle.
Elastic collisionInteraction between two objects in which kinetic energy is conserved.
Electric field strengthThe ratio of force exerted by an electric field on a test charge to the magnitude of the charge.
Emission spectrumThe spectrum produced by radiation from excited atoms.
Energy levelsThe discrete amounts of energy that an electron in an atom may have.
EntropyA measure of disorder in a system.
Excited stateAn energy level in an atom that is higher than the ground state.
FaradThe unit of capacitance. One farad equals one coulomb per volt.
First law of thermodynamicsThe change in internal energy is equal to heat added and work done on system.
Fundamental particlesThe smallest particles (quarks and leptons) of which all materials are composed.
GluonThe carrier particle of the strong nuclear force.
GravitonThe particle that carries the gravitational force. Not yet observed.
Heat engineA device that converts thermal energy to mechanical energy.
Heisenberg uncertainty principleThe more accurately the position of a particle is measured, the less accurately the momentum can be known, and vice versa.
ImpulseThe product of force and time interval over which it acts. Equals the change in momentum of an object.
Inelastic collisionCollision in which kinetic energy is not conserved.
LaserA device that produces coherent light by stimulated emission of radiation.
Law of universal gravitationThe gravitational force between two objects depends directly on the product of their masses and inversely on the square of their separation.
Lenz’s lawThe magnetic field generated by an induced current opposes the change in field that caused the current.
LeptonA “light” particle that does not interact with the strong nuclear force. Includes the electron and the neutrino.
Linear acceleratorA device that accelerates subatomic particles by applying successive electric field.
NeutrinoChargeless, massless, subatomic particle emitted in beta decay. A type of lepton.
Photoelectric effectThe ejection of electrons from surface of metal exposed to electromagnetic radiation.
PhotonA quantum of electromagnetic waves and a mediator of the electromagnetic interaction..
Photovoltaic cellA device that converts electromagnetic radiation into electrical energy.
Planck’s constantThe ratio of energy of photon to its frequency. A fundamental constant.
Principle of superpositionWhen two waves interact, the resulting amplitude is equal to the sum of the individual amplitudes of the two waves.
QuarkThe basic building blocks of protons, neutrons, other baryons, and mesons.
ResistivityA measure of how strongly a material opposes the flow of electric current.
Second law of thermodynamicsHeat always flows from a region of high temperature to a region of lower temperature.
Simple harmonic motionMotion caused by linear restoring force that is proportional to the square of the displacement, and that has a period independent of the amplitude of motion.
SuperconductorAn electrical conductor that has no resistance and low temperatures.
StrangenessA property of strange quarks. Strangeness is always conserved in strong interactions.
Strong nuclear forceForce of very short range that holds neutrons and protons in nucleus together. Mediated by gluons.
SynchrotronA device to accelerate particles in which particles move in circular path. Uses magnetic fields.
TransistorA semiconductor device that controls large current by means of small voltage changes.
Wave-particle dualityThe principle that matter can exhibit both particle and wave-like properties.
Weak nuclear forceThe force involved in beta decay of the neutron and atomic nuclei.
Work functionEnergy needed to remove an electron from metal. Mediated by bosons.
Young’s modulusA constant of proportionality associated with the change in length of a material according to its elastic properties.
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