Q. 133.8( 11 Votes )

(a) Draw the equipotential surfaces corresponding to a uniform electric field in the z-direction.

(b) Derive an expression for the electric potential at any point along the axial line of an electric dipole.

Answer :


Note that the electric field is always perpendicular to the equipotential surface. Hence, the equipotential surfaces are going to be infinite plane sheets parallel to the x-y plane.

Also, the electric field strength is proportional to the distance between the surfaces. Hence, the surfaces will be evenly spaced.


Let charge +q and -q be separated by distance 2a. Let origin be at the centre of the two charges. Consider any arbitrary point P (x,0).

Let ra be the distance of point P from the positive charge and rb be the distance of the point P from the negative charge.

The electric potential at point P is given by:

We have two cases:

Case I: and



Case II: and



Case III: and



Case IV:


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