![(a) A conductor A with a cavity as shown in Fig. 1.36(a) 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. 1.36(b)]. (c) A sensitive instrument is to be shielded from the strong electrostatic fields in its environment. Suggest a possible way](https://discussion.tiwariacademy.com/app/uploads/2021/02/F-1.36.png)
Class-12th Physics, CBSE and UP Board
Electric Charges and Fields,
Chapter-1,Exercise -1, Additional Exercise, Q-1.28
NCERT Solutions for Class 12th Physics
(a) A conductor A with a cavity as shown in Fig. 1.36(a) 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. 1.36(b)]. (c) A sensitive instrument is to be shielded from the strong electrostatic fields in its environment. Suggest a possible way
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Refer figure given in Question
Ans (a).
Let us consider a Gaussian surface that is lying wholly within a conductor and enclosing the cavity. The electric field intensity E inside the charged conductor is zero.
Let q be the charge inside the conductor and is ε0 the permittivity of free space.
According to Gauss’s law, Flux, φ = E. ds = q/ε0
Here, E = 0 => q/ε0 = 0 => q = 0 [as ε0 ≠ 0 ]
Therefore, charge inside the conductor is zero.
The entire charge Q appears on the outer surface of the conductor.
Ans (b).
The outer surface of conductor A has a charge of amount Q. Another conductor B having charge +q is kept inside conductor A and it is insulated from A. Hence, a charge of amount —q will be induced in the inner surface of conductor A and +q is induced on the outer surface of conductor A. Therefore, total charge on the outer surface of conductor A is Q + q.
Ans (c).
A sensitive instrument can be shielded from the strong electrostatic field in its environment by enclosing it fully inside a metallic surface. A closed metallic body acts as an electrostatic shield.