Absolute uncertainty - a quantity giving the extremes a measured value falls within

Absolute zero - the temperature at which all random motion of molecules stops

Absorption spectra - the set of wavelengths of photons absorbed by a substance

Ac generator - a rotating coil in a magnetic field that generates ac voltage

Acceleration of free fall - the acceleration due to the pull of the Earth on a body

Accurate - a measurements where the systematic error is small and so close to the ‘true’ value

Activity - the rate of decay of a radioactive sample

Albedo - the ratio of scattered to incident intensity of radiation

Alpha decay - a decay producing an alpha particle

Alpha particle - the nucleus of helium-4