Two point charges – q and + q are located at points (0, 0, - a) and (0, 0, a) respectively. The electric potential at a point (0, 0, z), where z > a is

Potential at P due to (+q) charge                 V1=14πε0.q(z−a)Potential at P due to (- q) charge                V2=14πε0.−q(z+a)Total potential at P duet to (AB) electric dipole              V=V1+V2                  =14πε0.q(z−a)−14πε0q(z+a)                  =q4πε0(z+a−z+a)(z−a)(z+a)⇒         V=2qa4πε0(z2−a2)