Two thin wire rings each having radius R are placed at distance d apart with their axes coinciding. The charges on the two are `+Q` and `-Q`. The potential difference between the centre so the two rings is

Options

A. zero
B. `Q/(4piepsilon_0) [1/R-1/(sqrt(R^2+d^2))]`
C. `Q/4piepsilon_0d^2)`
D. `Q/(2piepsilon_0)[1/R-1/(sqrt(R^2+d^2))]`

Answer

D

Explanation

`k=1/(4piepsilon_0)`
`V_(C_1)=(kQ)/R-(kQ)/(sqrt(R^2+d^2))`
`V-(C_2)=(kQ)/(sqrt(R^2+d^2))-(kQ)/R`
`:. V_(C_1)-V_(C_2)=Q/(2piepsilon_0)[1/R-1/(sqrt(R^2+d^2))]`