CGPET 2019 Solved Paper

Let the charge of small drop =q
Potential on small drop, V=

Kq

r

......(i)
When N identical spherical drops are combined to form a big drop, then volume remains constant.
N×

4

3

πr3=

4

3

πR3
where, R= radius of big drop.
R=(N1∕3)r
Potential of the new drop, V′=

K(Nq)

R

V′=

K(Nq)

(N1∕3)r

V′=

Kq

r

N1−

1

3

From Eq. (i), we get
V′=V.N

2

3