47 of the Physics glossary’s terms, each with the part of the syllabus where you first meet it.
Connecting a conductor to Earth so that electrons can flow between them, which neutralises the conductor or removes charge of one sign from it.
Loops of induced current that flow inside a solid piece of metal when the magnetic flux through it changes; they oppose the change and dissipate energy in the metal.
The curving and spreading of field lines near the ends of parallel plates, where the field is weaker and no longer uniform.
The ratio of useful work (or power) output to total work (or power) input, ; it has no unit and can never exceed 1 (100 %).
: the maximum kinetic energy of a photoelectron equals the energy of the absorbed photon minus the work function of the metal.
A collision in which both momentum and the total kinetic energy of the bodies are conserved.
The energy stored in a body because it is deformed. For a spring obeying Hooke's law,
A scalar property of particles such as protons and electrons that makes them exert electric forces on each other; it is positive or negative and measured in coulombs (C).
A closed conducting path through which charge can flow, containing a source of emf and components that transfer energy.
The rate of flow of charge past a point, ; measured in amperes (A), where .
A region in which a charge experiences an electric force.
The electric force per unit charge on a small positive test charge, ; a vector measured in or
The work done per unit charge in bringing a small positive test charge from infinity to a point, for a point charge; a scalar measured in volts.
The work done to assemble a system of charges from infinite separation; for two point charges
The sudden conduction of an insulator such as air when the electric field becomes strong enough to ionise it, producing a spark; for dry air about .
The production of an emf in a circuit when the magnetic flux linking it changes.
The continuous range of electromagnetic waves ordered by wavelength: gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves.
A transverse wave of electric and magnetic fields oscillating in phase, perpendicular to each other and to the direction of travel; it travels through a vacuum at .
The spreading and interference of an electron beam passing through or reflecting off a crystal, which shows that electrons have a wave nature.
A device that produces a narrow beam of electrons: electrons released from a heated cathode are accelerated through a potential difference towards an anode and pass through a hole in it.
A unit of energy: the energy transferred when one electron moves through a pd of 1 V; .
The separation of charge in a conductor caused by a nearby charged object; with earthing it charges the conductor, without contact, with the opposite sign to the object.
The magnitude of the charge on one electron or proton, .
A closed oval curve with two points inside it called foci; planetary orbits are ellipses with the Sun at one focus.
The energy transferred from other forms into electrical energy per unit charge passing through a source, symbol ; measured in volts.
A set of bright lines at particular wavelengths, produced by a hot gas at low pressure; each line comes from electrons dropping between two energy levels.
The power radiated per unit area by a surface divided by the power per unit area a black body at the same temperature would radiate, ; a number from 0 to 1.
A law found from experimental measurements that describes a pattern without explaining its cause.
The capacity of a system to do work; a scalar quantity measured in joules (J) that is conserved in every process.
The condition in which a planet (or part of it) radiates away energy at the same rate as it absorbs it, so its temperature stays constant.
The energy released by a fuel per unit volume, measured in .
One of the discrete values of energy that an electron in an atom is allowed to have.
The additional warming of the Earth's surface caused by increases in greenhouse gas concentrations due to human activity, mainly the burning of fossil fuels.
Uranium in which the fraction of uranium-235 has been raised above the natural 0.7%, to about 3–5% for most power reactors.
A property of the state of a system that measures its disorder; it changes by and equals ; measured in
The four equations linking , , , and for a body moving in a straight line with uniform acceleration.
The position where the resultant force on an oscillating body is zero; displacement in an oscillation or a wave is measured from it.
The temperature at which a planet radiates as much power as it absorbs; without an atmosphere it satisfies .
A surface on which every point has the same potential; no work is done moving along it, and field lines cross it at right angles.
A line through a plotted point that extends by the absolute uncertainty on each side, showing the range of the value.
The marking rule by which a wrong value is penalised only once: later work that uses it with a correct method still earns its marks.
The minimum launch speed for an unpowered object to escape completely from a body's gravitational field,
The change from liquid to gas at the surface of a liquid, at any temperature, as the fastest molecules escape; it cools the remaining liquid.
Something that happens at a single point in space at a single instant, described in a frame by one position and one time coordinate.
Any energy level of an atom above the ground state; an atom in an excited state soon drops to a lower level and emits a photon.
A planet orbiting a star other than the Sun; many are found from the periodic Doppler shift of their star's spectral lines.
An interaction in which bodies fly apart from rest or from each other; momentum is conserved while kinetic energy increases at the expense of another store.