Question -
Answer -
(a) Let us consider a Gaussiansurface that is lying wholly within a conductor and enclosing the cavity. Theelectric field intensity E inside the charged conductor iszero.
Let q isthe charge inside the conductor and 
is the permittivity of freespace.
According to Gauss’s law,
Flux, 
Here, E =0
Therefore, charge insidethe conductor is zero.
The entire charge Q appearson the outer surface of the conductor.
(b) The outer surface ofconductor A has a charge of amount Q. Another conductor B havingcharge +q is kept inside conductor A and it is insulated from A.Hence, a charge of amount −q will be induced in the inner surfaceof conductor A and +q is induced on the outer surface of conductorA. Therefore, total charge on the outer surface of conductor A is Q + q.
(c) A sensitive instrument canbe shielded from the strong electrostatic field in its environment by enclosingit fully inside a metallic surface. A closed metallic body acts as anelectrostatic shield.