(a) A conductor A with a cavity as shown in Fig, is given a charge Q. Show that the entire charge must appear on the outer surface of the conductor.
(b) Another conductor B with charge q is inserted into the cavity keeping B insulated from A. Show that the total charge on the outside surface of A is `(Q+q)` fig.
(c) A sensitive instrument is to be shielded from the strong electrostatic field in its environment. Suggest a possible way.

Explanation

(a) Visualise a Gaussian surface just inside the outer surface of the conductor. The electric field intensity everywhere on this Gaussian surface will be zero, The electric flux linked with the selected Gaussian surface becomes zero, hence as per Gauss.s law the net enclosed charge must be zero. Therefore whatever charge is given to the conductor, it will come to the outer surface of the conductor.
(b) The chargeq at the centre of the cavity induces -q charge on the inner surface of the cavity, thus q charge is induced on the outer surface of the conductor. The original charge with the conducting object was Q and therefore now Q+q charge will be distributed on the outer surface of the conductor.
(c )The region enclosed by the metallic object is electrostatically shielded. So, we need to cover the instrument by a metal surface from all sides. The cavity inside the conductor can be ued for this purpose.