66 of the Physics glossary’s terms, each with the part of the syllabus where you first meet it.
A transverse seismic wave; it travels more slowly than P waves and cannot pass through liquids.
A diagram of energy transfers in which the width of each arrow is proportional to the energy or power it represents; useful output runs straight on and wasted energy branches away.
The largest photocurrent from a photocell, reached when every photoelectron emitted is collected by the anode; it is proportional to the photon flux.
A quantity that has magnitude only, such as distance, speed, mass or time.
The entropy of an isolated system never decreases; equivalently, thermal energy does not flow spontaneously from cold to hot, and no cyclic engine converts thermal energy completely into work.
A rechargeable chemical cell, such as a lithium-ion or lead–acid cell, whose reactions are reversed by driving a current backwards through it.
Data collected by someone else and selected by the investigator, for example from a published database.
A wave that carries energy through the Earth from an earthquake or explosion.
The emf induced in a coil by a change in its own current, which changes its own flux linkage; by Lenz’s law it opposes the change in current.
Half the longest diameter of an ellipse; for an orbit, the mean of the closest and farthest distances from the central body.
A material such as silicon with few mobile charge carriers, whose number increases when it is heated or illuminated, so its resistance falls.
Components joined end to end so that there is one path for the current: they share the same current and their pds add.
Material such as steel, water and concrete around a reactor that absorbs neutrons and gamma radiation to protect people.
The cone-shaped pile-up of wavefronts produced by a source moving faster than the waves it emits, heard for sound as a sonic boom.
A connection of negligible resistance across a source, giving the largest possible current, .
One of the seven independent units of the International System (kg, m, s, A, K, mol, cd) from which every other SI unit is derived.
A symbol placed before a unit to multiply it by a power of ten, such as k for or μ for .
A digit in a number that carries information about its precision; leading zeros are not significant, trailing zeros after a decimal point are.
Oscillation in which the acceleration is proportional to the displacement from a fixed equilibrium position and always directed towards it: .
A small dense bob on a light inextensible string that, for small angles, oscillates with simple harmonic motion of period .
A computer model of a physical system in which the investigator sets the inputs and records the outputs as data.
A simple energy-balance model in which the atmosphere is one layer of uniform temperature and emissivity, transparent to sunlight, that exchanges infrared with the surface and space.
A metal ring on the axle of a generator, connected to one end of the coil, on which a fixed brush slides so that the coil stays connected to the external circuit as it turns.
For an angle in radians that is small (below about 0.2 rad), .
For a wave refracted at a boundary,
A semiconductor device that converts the energy of light directly into electrical energy; a source of emf.
The intensity of the Sun's radiation at the Earth's mean distance from the Sun, on a surface perpendicular to the radiation outside the atmosphere: .
The continuous stream of charged particles, mainly protons and electrons, flowing outwards from the Sun.
A long coil of wire wound as a helix; a current in it produces a strong, uniform magnetic field inside and a field like a bar magnet's outside.
A longitudinal mechanical wave of compressions and rarefactions; it needs a medium and cannot travel through a vacuum.
Space and time combined into one framework in which every event is a point, needed because the Lorentz transformation mixes position and time.
A graph of events with position on the horizontal axis and on the vertical axis, on which light travels at 45°.
The quantity given by
A space-time interval with : not even light can link the events, so neither can cause the other and observers can disagree on their order.
Einstein's theory, based on two postulates, of how measurements of space and time made in different inertial reference frames are related.
The energy released by a fuel per unit mass, measured in .
The energy needed to raise the temperature of 1 kg of a substance by 1 K, ; measured in .
The energy needed to change the phase of 1 kg of a substance at constant temperature, ; measured in .
The energy needed to melt 1 kg of a solid at its melting point without changing its temperature (released again on freezing).
The energy needed to turn 1 kg of a liquid into gas at its boiling point without changing its temperature (released again on condensing).
A narrow bright or dark line in a spectrum at a wavelength emitted or absorbed by a particular element; its shift from the laboratory wavelength measures the radial velocity of the source.
The measurement of the wavelengths and intensities in a spectrum, used to identify the elements in a source of light or in a gas the light has passed through.
The range of wavelengths present in light (or other radiation) when they are spread out and separated, for example by a prism or a diffraction grating.
The rate of change of distance travelled; a scalar quantity measured in . It is the magnitude of the velocity.
Fuel removed from a reactor after use, containing unused uranium, highly radioactive fission products and plutonium.
Fission of an unstable heavy nucleus that happens on its own, randomly, without being triggered by an incoming particle.
The force per unit extension of a spring obeying Hooke's law, , measured in ; a stiffer spring has a larger .
A way of writing a number as , where and is an integer.
The pattern formed when two waves of the same frequency, wavelength and amplitude travelling in opposite directions superpose; it oscillates in place and transfers no net energy.
One of the measurable quantities that fix the state of a gas: pressure, volume, temperature and amount of substance.
The state of a rigid body that is at rest with zero resultant force and zero resultant torque on it.
Friction between surfaces that are not sliding; it matches the applied force up to a maximum value, .
The constant in the Stefan–Boltzmann law.
The total power radiated by a black body is proportional to its surface area and to the fourth power of its kelvin temperature: .
The state of a stable star in which, at every depth, the outward force from gas and radiation pressure balances the inward gravitational force.
The apparent shift of a nearby star against distant stars as Earth orbits the Sun; the parallax angle is the angle subtended at the star by 1 AU.
The viscous drag on a small sphere moving slowly through a fluid in laminar flow, , proportional to the radius, the speed and the viscosity.
The total distance a vehicle travels from the moment the driver sees a hazard until it stops: thinking distance plus braking distance.
The minimum reverse potential difference between anode and cathode that reduces the photocurrent to zero; .
The short-range (about ) attractive force between nucleons that holds the nucleus together against the electric repulsion of the protons.
A very large and very luminous star, at the top of the HR diagram, formed when a massive star leaves the main sequence.
The explosion of a massive star at the end of its life, when its iron core collapses, leaving a neutron star or a black hole.
Everything outside the thermodynamic system being studied, with which the system can exchange energy.
The positive feedback in which pedestrians on a swaying footbridge fall into step with the sway, so their sideways foot forces increase it.
An exam question that combines ideas from two or more areas of the course in one context.
An error that shifts every reading in the same direction by the same amount or proportion; repeating measurements does not reduce it.