Physics key terms

The amount of ionising radiation absorbed by matter, such as body tissue.

Radiation taken in by a body, transferring energy to it.

An object or material that takes in energy carried by a wave.

The transfer of a wave’s energy to a material as the wave passes into it.

A dark line at a particular wavelength in a continuous spectrum, produced when an element absorbs that wavelength.

A pattern of dark lines produced when particular wavelengths are absorbed from a continuous spectrum.

The rate at which velocity changes. It is measured in metres per second squared, m/s².

The acceleration of a freely falling object caused by gravity; near Earth's surface its magnitude is taken as 10 m/s² for this course.

The acceleration of an object falling under gravity alone; near Earth's surface its magnitude is approximately 9.8 m/s².

The closeness of a measurement to the true value.

Rain made more acidic by pollutants in the atmosphere, including sulfur dioxide from burning sulfur-containing fuels.

The rate at which unstable nuclei decay in a radioactive source.

A graph showing how activity, count rate or the number of undecayed nuclei changes with time.

A conducting rod or wire used to transmit or receive radio waves.

A conductor used to transmit or receive electromagnetic waves.

The proportion of incoming radiation reflected by a surface.

A particle consisting of two protons and two neutrons, represented as $^4_2\text{He}$ or $^4_2\alpha$.

An experiment in which alpha particles were directed at thin metal foil and their scattering was observed.

Radiation consisting of helium nuclei, each containing two protons and two neutrons.

A current that repeatedly reverses direction.

Current that repeatedly reverses direction.

A potential difference whose polarity repeatedly reverses, usually while its magnitude also varies.

A potential difference that repeatedly reverses polarity, usually changing continuously with time.

A voltage whose polarity repeatedly reverses, so each terminal alternates between being positive and negative relative to the other.

A generator that produces alternating current.

Height above a reference level, such as sea level.

A meter connected in series to measure current in amperes.

The unit of electric current. One ampere means that one coulomb of charge passes a point each second.