Question

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

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

Answer 1

The correct option is C $Q=-q$

Let the side of the square be $=a$

Potential at centre

$V_c=\frac{K\times -Q}{\frac{a}{\sqrt{2}}}+\frac{K\times -q}{\frac{a}{\sqrt{2}}}+\frac{K\times 2q}{\frac{a}{\sqrt{2}}}+\frac{K\times 2Q}{\frac{a}{\sqrt{2}}}$

$0=\frac{KQ}{\frac{a}{\sqrt{2}}}+\frac{Kq}{\frac{a}{\sqrt{2}}}$

$\Rightarrow Q=-q$

Option (C) is correct