Question

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

Answer 1

Correct Answer - B
If potential at centre is zero, then
`V_(1)+V_(2)+V_(3)+V_(4) = 0`
`-(kQ)/(r ) - (kq)/(r ) + (k2Q)/(r ) + (k2q)/(r ) = 0`
`-Q - q + 2q + 2Q = 0`
`Q = -q`