In pictorial form, this electric field is shown as "lines of flux" being radiated from a dot (the charge).
The density of these lines corresponds to the electric field strength, which could also be called the electric flux density: the number of "lines" per unit area.
For simplicity in calculations it is often convenient to consider a surface perpendicular to the flux lines.
For a closed Gaussian surface, electric flux is given by: where This relation is known as Gauss's law for electric fields in its integral form and it is one of Maxwell's equations.
While the electric flux is not affected by charges that are not within the closed surface, the net electric field, E can be affected by charges that lie outside the closed surface.
While Gauss's law holds for all situations, it is most useful for "by hand" calculations when high degrees of symmetry exist in the electric field.
The SI unit of electric flux is the volt-meter (V·m), or, equivalently, newton-meter squared per coulomb (N·m2·C−1).