question_answer

A sphere of 4 cm radius is suspended within a hollow sphere of 6 cm radius. The inner sphere is charged to potential 3 e.s.u. and the outer sphere is earthed. The charge on the inner sphere is                                          [MP PMT 1991]

A)            54 e.s.u.

B)                                      \[\frac{1}{4}\] e.s.u.

C)            30 e.s.u.

D)                                      36 e.s.u.

Correct Answer: D

Solution :

                     Suppose charge on inner sphere is +Q as shown. Potential on inner sphere \[V=\frac{Q}{4}-\frac{Q}{6}\] Þ \[3=Q\,\left( \frac{1}{4}-\frac{1}{6} \right)\] Þ \[Q=36\,e.s.u.\]