Capacity of an isolated conducting sphere is increased by 3 times when it is enclosed with in an ear

Question

Capacity of an isolated conducting sphere is increased by 3 times when it is enclosed with in an earthed concentric sphere. The ratio of their radii is\

Professor PC Thomas Classes · Answer

$\frac{\mathrm{b}}{\mathrm{a}}=\frac{\mathrm{n}}{\mathrm{n}-1}$ then $\mathrm{n}=3$\