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

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

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

Similarly, the electric field E at a point r relative to the point charge in cgs is given by

In MKS, the corresponding equation is

where is a fundamental constant called the permittivity of free space. This function is plotted as the vector field in the right figure above.