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inverse-square law[′in‚vərs ¦skwer ‚lȯ]
Any law in which a physical quantity varies with distance from a source inversely as the square of that distance.
A law which applies to a light source (or to a sound source) that is in a space far away from any reflecting surface: the intensity at a point, as measured on a surface which is perpendicular to a line drawn between the point and the source, varies inversely with the square of the distance between the point and the source. (For sound waves, this decrease in intensity is equivalent to a drop in sound-pressure level of 6 dB for each doubling of distance from the source.)