Question

Shown in the figure are two point charges $+\, Q$ and $— Q$ inside the cavity of a spherical shell. The charges are kept near the surface of the cavity on opposite sides of the centre of the shell. If $\sigma_{1}$ is the surface charge on the inner surface and $Q_1$ net charge on it and $\sigma_{2}$ the surface charge on the outer surface and $Q_2$ net charge on it then :

• A. $\sigma_{1} \ne 0, \, Q_{1} \ne 0; \sigma_{2} \ne 0,\, Q_{2} \ne 0$
• B. $\sigma_{1} \ne 0, \, Q_{1} = 0; \sigma_{2} \ne 0,\, Q_{2} = 0$
• C. $\sigma_{1} \ne 0, \, Q_{1} = 0; \sigma_{2} = 0,\, Q_{2} = 0$
• D. $\sigma_{1} = 0, \, Q_{1} = 0; \sigma_{2} = 0,\, Q_{2} = 0$

Answer 1

Answer: (D)

Net charge inside the cavity is zero.
Net charge inside the cavity is zero.
$
\therefore Q _{1}=0 \text { and } \sigma_{1}=0
$
There is no effect of $+Q,-Q$ and induced charge on inner surface on the outer surface hence
$
Q _{2}=0, \sigma_{2}=0
$