Electrostatic shell theorem ($\mathbf{E}(r)=Q{\mathbf{e}}_r/(4\pi {ϵ}_0{r}^2)$)

Outside a bounded spherically symmetric charge distribution in vacuum, the electric field is that of a central point charge with the same total electric charge. With zero electric potential at infinity, the exterior electric potential is $Q/(4\pi {ϵ}_{0}r)$. A uniform surface charge on a sphere has zero electric field inside.