Question

Four identical point charges +q each are placed at the four corners (one q at one corner) of a square of side 1. Find the force experienced by a test charge q0 placed at the center of the square

Answer 1

no force is experienced by qo charge because resulting forces cancel out each other

Answer 2

The force experienced by a test charge q0(whatever maybe) placed at the centre of the square is Zero
Reason:The resultant force of the point charges direct along the diagonal of the square ,Hence Cancelling the effect.

This phenomenon works only if there are identical point charges at same distance from the centre