Each corner of a cube of side l has a negative charge,

Each corner of a cube of side l has a negative charge, –q. The electrostatic potential energy of a charge q at the centre of the cube is

Length of body diagonal = √3l
∴ Distance of centre of cube from each corner

r =	√3	l
	2

P.E. at centre
= 8 × Potential Energy due to A

= 8 ×	√3	l
	2

= 8 ×	1	× 2 × q × (-q) =	-4q²
	4πε₀√3l		√3πε₀l

-	4q²
	√3πε₀l