# Dictionary:Inverse-square law

**1**. The magnitude of a potential field U surrounding a unit element varies inversely as the square of the distance from the element *m*:

Applies to a gravitational field where the element *m* is mass and *k* is the *gravitational constant* (q.v.); to a magnetic field where the element *m* is a magnetic pole of strength *m* in ampere meters and *k* is 10^{–7} webers/amperemeter; and to an electrostatic field where the element *m* is an electrical charge of *m* coulombs and *k* is 9×10^{9} newtons/coulomb. For the gravity case, the relation is called **Newton’s law of universal gravitation** and for the electrostatic case it is called **Coulomb’s law. 2**. The energy density of a seismic body wave from a point source in a homogeneous isotropic medium varies inversely as the square of the distance from the point source. Also called **spherical divergence. 3**. The intensity of electromagnetic energy (light or radio) varies inversely as the square of the distance from a source.