Question

It is required to hold equal charges q in equilibrium at the corners of a square

Answer 1

Explanation:

Each of corners of square has charge +q. ... Clearly, charge Q has to be negative in nature to hold charges +q in equilibrium. If the net force on a charge +q at any corner (say A) is zero, then by symmetry it follows that the net force experienced by the other charges at other corners will also be zero.