In the figure charges are enclosed by spherical surfaces $S_1$ and $S_2$  If the electric flux through surface $S_2$ is four times that of electric flux through$S_1$, find relation between $Q$ and $q$.

State Gauss’ theorem in electrostatics.
Apply this theorem to derive an expression for the electric intensity due to an infinite sheet of charge and hence deduce the expression for electric intensity due to two parallel oppositely charged thin infinite sheets of charge at a point

(i) between the sheets,

State Gauss’ theorem in electrostatics.
Apply this theorem to derive an expression for the electric intensity due to an infinite sheet of charge and hence deduce the expression for electric intensity due to two parallel oppositely charged thin infinite sheets of charge at a point

(ii) Outside the sheets.