Question

27 spherical droplets of radius 3um and each carry 10^-12C of charge are combined to form a bigger drop find capacitance of bigger drop

Answer 1

Conserving the volume of both the spheres..we have..

4/3πr³ *27 = 4/3πR³
Solving this eqn we get
R=3r = 3 mm

Now the total charge on 27 drops= 27*10^-12

Therefore potential on the surface of the big drop = kq/r
= 9*10⁹ * 27*10^-123*10^-3
=81 V

Capacitance=q/V=(27*10^-12)/81
C=1/3pF