A solid spherical conductor of radius $\mathrm{R}$ has a spherical cavity of radius $a(a < R)$ at its centre. A charge $+Q$ is kept at the centre. The charge at the inner surface, outer surface and at a position $r(a < r < R)$ are respectively

• A

  $+Q,-Q, 0$
• Correct answer
  B

  $-Q,+Q, 0$
• C

  $0,-\mathrm{Q}, 0$
• D

  $+Q, 0,0$

Solution

A charge $Q$ will be induced on the inner surface of the solid spherical conductor. An equal but opposite charge will be induced on the outer surface of the conductor. There will be no charge at a position between the inner and outer surface.

Hence, the correct answer is option: 'B'.