A point charge is a hypothetical charge located at a single point in space. While an electron can for many purposes be considered a point charge, its size can be characterized by length scale known as the electron radius.
In cgs, the magnetic field at a point r of a slowly moving charge q at position is given by


where v is the charge's velocity and c is the speed of light, and in MKS,

The magnetic and electric fields of a moving charge are related in cgs by

and in MKS by

For relativistic speeds, from the Liénard-Wiechert potentials, it follows that




where is relativistic beta and a is the acceleration.