Four point charges `-Q, -q, 2q` and `2Q` are placed, one at each corner of the square. The relation between `Q` and `q` for which the potential at the centre of the square is zero is

Options

A. Q = q
B. `Q = -1/q`
C. Q = q
D. `Q = 1/ q`

Answer

A

Explanation

V = 0
`implies (K(-Q))/(a/sqrt2)+(K(-q))/(a//sqrt2)+(K(2q))/(a//sqrt2)+(K(2Q))/(a//sqrt2)=0`
`implies -Q -q + 2q + 2Q = 0 implies Q =-q`