Two charges - q and +q are located at points (0, 0, - a) and (0,0, a), respectively.
What is the electrostatic potential at the points (0, 0, z) and (x, y,0) ?

Explanation

The given charges behave as an electric dipole and the dipole length is 2a, hence dipole moment `p = q.2a`.
For given dipole, point (0,0, z) lies at the axial line at a distance z from the mid-point of dipole. Hence
`V = 1/(4pi epsi_0).p/((z^2-a^2))`
However, the point (x, y,0) lies at the equatorial line of dipole and hence electric potential at this point is zero.