Show that the excess charge on a conductor resides only on its surface.

Show that the electric field at the surface of a charged conductor is given by $\overrightarrow{E}=\frac{\sigma }{{\epsilon }_0}\widehat{n}$, where $\sigma$ is the surface charge density and n ̂ is a unit vector normal to the surface in the outward direction?

or

Derive an expression for the electric field at the surface of a charged conductor.