20 of the Physics glossary’s terms, each with the part of the syllabus where you first meet it.
Ionising radiation present everywhere from natural and artificial sources (radon, rocks, cosmic rays, food, medical uses), which must be subtracted from measured count rates.
The narrow region of a plot of neutron number against proton number where the stable nuclides lie; it follows for light nuclei and curves to for heavy ones.
Two or more cells connected in series.
The SI unit of activity: one decay per second.
A decay in which a neutron in the nucleus changes into a proton, and an electron (β⁻ particle) and an antineutrino are emitted.
A decay in which a proton in the nucleus changes into a neutron, and a positron (β⁺ particle) and a neutrino are emitted.
The energy needed to separate a nucleus completely into its individual protons and neutrons; equal to the mass defect times .
The binding energy of a nucleus divided by its nucleon number; the larger it is, the more tightly bound the nucleus.
An idealised object that absorbs all radiation falling on it and emits the maximum possible radiation at each wavelength, with a spectrum set only by its temperature.
A region of space where matter has collapsed so far that its gravity prevents anything, even light, from escaping; formed from the cores of the most massive stars.
A decrease in the observed wavelength (and increase in frequency) of electromagnetic waves from a source moving towards the observer.
Bohr's model of the hydrogen atom: the electron moves in circular orbits whose angular momentum is quantised, , and emits or absorbs a photon only when it jumps between orbits.
The radius of the smallest () orbit in the Bohr model of hydrogen, about m.
The change from liquid to gas throughout the liquid, with bubbles of vapour forming, at a fixed temperature for a given pressure.
The gas constant per molecule,
The condition a standing wave must meet at the end of its medium: a node at a fixed or closed end, an antinode at a free or open end.
For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume: = constant.
The distance a vehicle travels from the moment the brakes are applied until it stops; for a constant deceleration it is proportional to the square of the initial speed.
The random, jerky movement of small particles suspended in a fluid, caused by uneven bombardment by the fluid's molecules.
The upward force of a fluid on a body in it, equal to the weight of fluid displaced: .