Q. A large insulated sphere of radius $r$ charged with $Q$ units of electricity is placed in contact with a small insulated uncharged sphere of radius $r'$ and in then separated. The charge on smaller sphere will now be
A) $Q(r + r')$
B) $\frac{Qr'}{r^{'} + \ r}$
C) $Q(r - r')$
D) $\frac{Q}{r^{'} + \ r}$
Explanation
(b) Common potential,
$V = \frac{total\ charge}{total\ capacity} = \frac{Q + 0}{4\pi\varepsilon_{0}\left( r + r^{'} \right)}$
$\therefore\ $ charge on smaller sphere
$= 4\pi\varepsilon_{0}r^{'} \times V = \frac{Qr'}{r + r'}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.