Four equal charges Q are placed at the four corners of a square of each side ‘a’ . Work done in removing a charge –Q from its center to infinity is

Potential at center O of the square Vo=V1+V2+V3+V4=4V=4Q4πε0r=4Q4πε0a/2∵r=a2Work done in shifting (-Q) charge from center to infinityW=−QV∞−VO=QV0 =42Q24πε0a=2Q2πε0a.