In physics, **Coulomb's law** is an inverse-square law indicating the magnitude and direction of electrical force that one stationary, electrically charged substance of small volume exerts on another. When one is interested only in the magnitude of the force (and not in its direction), it may be easiest to consider a simplified, scalar version of the Law

*q*

_{1}is the charge on one substance,

*q*

_{2}is the charge on the other,

*r*is the distance between them, and ε

_{0}is a universal constant, the permittivity of vacuum. (See physical constants for more information. Note that 1/(μ

_{0}ε

_{0}) = c

^{2}