Q. 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
A) $54e.s.u.$
B) $1/4e.s.u.$
C) $30e.s.u.$
D) $36e.s.u.$
Explanation
(d) Suppose charge on inner sphere is $+ Q$ as shown. Potential on inner sphere
$V = \frac{Q}{4} - \frac{Q}{6}$
$\Rightarrow 3 = Q\left( \frac{1}{4} - \frac{1}{6} \right) \Rightarrow Q = 36\ e.s.u$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.