The surface density on the copper sphere is $$\sigma .$$ The electric field strength on the surface of the sphere is

Solution :
According to Gauss's theorem,
$$\eqalign{ & E\oint {ds} = \frac{q}{{{ \in _0}}}\,\left[ {{\text{Here}}\,E\oint {ds} = 4\pi {R^2}} \right] \cr & \therefore E = \frac{{\frac{q}{{4\pi {R^2}}}}}{{{ \in _0}}}\,\left[ {\because \frac{q}{{4\pi {R^2}}} = \sigma } \right] \cr & {\text{or}}\,\,E = \frac{\sigma }{{{\varepsilon _0}}} \cr} $$