Four electric charges +q, +q, –q and

Four electric charges +q, +q, –q and – q are placed at the corners of a square of side 2L (see figure). The electric potential at point A, midway between the two charges +q and +q, is

Distance of point A from the two +q charges = L. Distance of point A from the two –q charges = = .
= √L² + (2L)²
= √5L

∴ V_A =		Kq	× 2		-		Kq	× 2
		L					√5L

=	2Kq		1 -	1
	L			√5

=	1	.	2q		1 -	1
	4πε₀		L			√5

1	2q	(1 + √5)
4πε₀	L	(1 + √5)