Equal potential (or equipotential) lines refer to regions of equal potential. Equipotential lines are always perpendicular to the electric field. In three dimensions, the lines form equipotential surfaces, as shown in the Figure 2 below.

Figure 2

The equal potential surface has the following characteristic:

1. No work done to move a charge between two points on the same equal potential surface.

2. Electrical field lines are perpendicular to equal potential surfaces.

3. The surface of a conductor is an equal potential surface.