Question

A metallic spherical shell has an inner radius $R_{1}$and outer radius $R_{2}.$ A charge is placed at the centre of the spherical cavity. The surface charge density on the inner surface is.

• A. $\frac{q}{4\pi R_{1}^{2}}$
• B. $\frac{- q}{4\pi R_{1}^{2}}$
• C. $\frac{q^{2}}{4\pi R_{2}^{2}}$
• D. $\frac{2q}{4\pi R_{2}^{2}}$

Answer 1

Answer: (B)

$\frac{- q}{4\pi R_{1}^{2}}$

Answer 2

: When a charge + q is placed at the centre of spherical cavity as shown in Figur

Charge induced on the inner surface of shell

= + q …(i)

Charge induced on the outer surface of shell

= + q …(ii)

$\therefore$Surface charge density on the inner surface$= \frac{- q}{4\pi R_{1}^{2}}$