There are four concentric shells A,B, C and D of radii `a,2a,3a` and `4a` respectively. Shells B and D are given charges `+q` and `-q` respectively. Shell C is now earthed. The potential difference `V_A-V_C` is `k=(1/(4piepsilon_0))`

Options

A. `(Kq)/(2a)`
B. `(Kq)/(3a)`
C. `(Kq)/(4a)`
D. `(Kq)/(6a)`

Answer

D

Explanation

Potential at `C=(Kq)/(3a)-(Kq)/(4a)+(Kq')/(3a)=0rArr q'=-q/4`
Potential at `A=(Kq)/(2a)-(Kq)/(4a)-(Kq/4)/(3a)=(Kq)/(6a)`
Hence `V_(A)-V_(C)=(Kq)/(6a)`