Let us consider a charged hollow sphere with charge q. The charge q is on the surface of the sphere. We have to calculate the electric field at an interior point P distance r from the centre. If we imagine a Gaussian spherical surface through the point P and concentric with the given shell, we can use the Gauss theorem, E×4πr2=E0q′ where q' is the charge enclosed by this Gaussian surface = 0 ∴E=0