For an electric charge q (i.e., an electric monopole), the voltage (a.k.a. electric potential) in cgs is given by

(1)

where r is the distance from the charge. In MKS, the corresponding formula is

(2)

where is the permittivity of free space. This function is plotted in the left figure above.

Electric Dipole, Electric Field, Electric Multipole Expansion, Magnetic Monopole, Point Charge