(physics, optics) one of several
laws relating two quantities such that one
quantity varies inversely as the
square of the other. There are
laws using this
basic principle which apply to magnetism,
sound and light. An
example of this would be that of the illumination produced on a
screen by a
point source of light: if the distance between the light
source and
screen were doubled, the illumination on the
screen would be reduced to a
quarter of its original intensity; if the distance were trebled, the illumination would be reduced to one-ninth; if the distance were quadrupled, the illumination would be reduced to one-sixteenth, etc. Likewise, the intensity of
sound decreases as the distance from its
source increases: a bell 10 feet away sounds one-
fourth as
loud as the same bell 5 feet away; and if 15 feet away, it sounds one-ninth a s
loud as when 5 feet away. Applied to
radiation, the inverse
square law states that the intensity of
radiation decreases in proportion to the
square of the distance from its
source.
—All About Radiation Glossary. Final approval 27.9.89