physics
posted by H .
A positive point charge and a negative point charge have equal magnitudes. One charge is fixed to one corner of a square, and the other is fixed to another corner. On which corners should the charges be placed, so that the same potential exists at the empty corners? What is the reasoning?

The two charges should be placed at diagonally opposite corners, because in that case the open corners are equidistant from the positive and the negative charges, so there is no effect on the potential there.

Electrical potential is the force experienced by a unit test charge at a particular point. In this case that potential on the test charge is generated by the positive and the negative charges placed in the two corners of the square.
There are two possible configurations for the "occupied" corner charges: Adjacent and diagonal. One of these configurations would produce identical effects on the test charge no matter which unoccupied corner it was placed on. Do some drawing and i think you will "see" which arrangement works best.