An equipotential surface is a surface where all the points lying on the surface have the same electric potential. In other words, it is a surface that has a constant value of potential throughout. The electric potential at a point is equal to the potential energy of a unit charge placed at that point. The direction of the electric field is perpendicular to the equipotential surface. The spacing between equipotential surfaces enables us to identify regions of a strong and weak field. Some key properties of equipotential surfaces are:

• All points on an equipotential surface have the same electric potential.
• The electric force neither helps nor hinders motion of a charge on an equipotential surface.
• For a point charge, the equipotential surfaces are concentric spherical shells.
• For a uniform electric field, the equipotential surfaces are planes normal to the x-axis.
• The equipotential surface for a point charge q is a sphere with the charge at its center.
• In a uniform electric field, any plane normal to the field direction is an equipotential surface.

Equipotential surfaces are a useful way to represent the potential distribution in an electric field graphically. They can be represented in two dimensions using lines to help us quantitatively visualize the electric potential in the region.