Four point charges -Q,-q, 2q and 2Q are placed, one at each comer of the square. The relation between Q and q for which the potential at the centre of the square is zero, is
A)\[Q=-q\]
B)\[Q=-\frac{1}{q}\]
C) \[Q=q\]
D) \[Q=\frac{1}{q}\]
Correct Answer:
A
Solution :
If potential at centre is zero, then \[{{V}_{1}}+{{V}_{2}}+{{V}_{3}}+{{V}_{4}}=0\] \[-\frac{kQ}{r}-\frac{kq}{r}+\frac{k2Q}{r}+\frac{k2q}{r}=0\] \[-Q-q+2q+2Q=0\] \[Q=-q\]