Inverse square law

From Ganfyd

As in the strength of electromagnetic radiation in proportion to the inverse square of the distance from the source.

Not to be confused with the Inverse care law. It also applies to gravity, acoustics (sound intensity), electrical and magnetic fields (with regard to energy and intensity, Coulomb's law in electrostatics) and follows from the divergence theorem (generalised Gauss's theorem) with fluxes and point source assumptions.