Explanation

(b) An equipotential surface is a surface with a constant value of potential at all points on the surface. For a uniform electric field, say, along the $x$-axis, the equipotential
surfaces are planes normal to the $x$-axis, $i.e.,$ planes parallel to the $y - z$ plane. Equipotential surfaces for a dipole and its electric field lines are shown in figure.
[image:1_image253.emf]
As said above that on equipotential surface, potential at all points is constant, this means that on equipotential surface work done in moving a test charge from one point to other point is zero.