Question

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

• A. $Q=q$
• B. $Q=\frac{1}{q}$
• C. $Q=-q$
• D. $Q=-\frac{1}{q}$

Answer 1

The correct option is C $Q=-q$

Since the potential at the center is zero:

$V=\frac{k}{r}(2q+2Q-q-Q)=0$ where r is distance of vertex from center of square.

$q+Q=0$

$Q=-q$