Question

A thick metallic spherical shell of inner radius $ r_1 $ and outer radius $ r_2 $ has a charge $ +Q $ . A charge $ +q $ is placed at the centre of the shell. The charge per unit area on the outer surface is

• A. $ \frac{\left(Q-q\right)}{4\pi\left(r_{2}^{2} - r_{1}^{2}\right)} $
• B. $ \frac{\left(Q-q\right)}{4\pi r_{2}^{2} } $
• C. $ \frac{\left(Q+q\right)}{4\pi r_{2}^{2} } $
• D. $ \frac{\left(Q+q\right)}{4\pi \left(r_{2}^{2}+r_{2}^{2}\right) } $

Answer 1

Answer: (C)

Charge on the outer surface $= Q + q$
$\therefore $ The charge per unit area $ = \frac{Q +q}{4 \pi r_2^2}$