36 of the Physics glossary’s terms, each with the part of the syllabus where you first meet it.
A graph of the current through a component against the pd across it.
A positive feedback in which warming melts ice and snow, exposing darker ocean and land that absorb more sunlight, which causes further warming.
A gas that obeys exactly; modelled by kinetic theory as point molecules with no forces between them except in elastic collisions.
The equation linking the pressure, volume, temperature and amount of an ideal gas.
A meter that does not change the circuit it measures: an ideal ammeter has zero resistance and an ideal voltmeter infinite resistance.
The perpendicular distance between the line along which a particle approaches and a parallel line through the centre of the nucleus; the smaller it is, the larger the deflection.
The product of the average resultant force on a body and the time it acts, ; it equals the change in momentum and the area under a force–time graph.
Two oscillations of the same frequency are in phase when their phase difference is zero, so they reach their maxima at the same time.
The variable that the investigator deliberately changes (or selects) to see its effect on another variable; it is plotted on the horizontal axis.
A current driven round a complete circuit by an induced emf, .
A cooker in which a rapidly alternating magnetic field from a coil induces eddy currents in the metal base of a pan, heating the pan directly.
A collision in which momentum is conserved but kinetic energy decreases; in a perfectly inelastic collision the bodies stick together.
The tendency of a body to resist changes to its velocity; the mass of a body is a measure of its inertia.
A reference frame that is not accelerating, in which a body with no resultant force on it stays at rest or moves with constant velocity.
Electromagnetic radiation with wavelengths from about 700 nm to 1 mm, longer than visible light; bodies at everyday temperatures emit mostly infrared.
A narrow, nearly vertical band of the HR diagram, at surface temperatures of roughly 5000–8000 K, in which evolved stars pulsate, regularly changing in size and luminosity.
The velocity of a body at one instant; on a displacement–time graph, the gradient of the tangent at that time.
A material with almost no mobile charge carriers, so that the current through it is negligible.
The power carried by a wave per unit area perpendicular to its direction of travel, in ; for a given frequency it is proportional to the square of the amplitude.
The superposition of waves from coherent sources, giving a steady pattern of maxima and minima.
The forces between the particles of a substance: attractive at moderate separations and strongly repulsive when particles are pushed very close together.
The total of the random kinetic energies and intermolecular potential energies of the particles in a substance.
The resistance of the materials inside a source of emf, symbol , which causes the terminal pd to fall below the emf when a current flows.
A quantity that has the same value in every inertial reference frame, such as the speed of light or the space-time interval.
A curve on a space-time diagram joining events with the same interval from the origin, used to mark equal units on the axes of different frames.
A relationship in which a quantity is inversely proportional to the square of the distance from a point source, as when radiation spreads over a sphere of area .
The minimum energy needed to remove an electron from an atom in its ground state; 13.6 eV for hydrogen.
Radiation with enough energy to remove electrons from atoms it passes, leaving ions; α, β and γ radiation are ionising.
A real process that cannot be exactly undone, because of friction, free expansion or heat flow across a temperature difference; it increases the total entropy.
A change at constant pressure, in which the work done by the gas is .
Describes an oscillation whose period does not depend on its amplitude, as in simple harmonic motion.
A system on which no resultant external force acts, so its total momentum stays constant.
A curve on a P–V diagram joining states of a gas at the same temperature; for an ideal gas, = constant along it.
A change at constant temperature; for an ideal gas , so .
One of two or more nuclides of the same element: the same proton number but different numbers of neutrons, and so different nucleon numbers.
A change at constant volume, in which the gas does no work, so .