A surface over all of which the potential is the same. In a general
sense equipotential surfaces are given by planes or surfaces which cut
lines of force at right angles thereto, or which are normal to lines of
force. The conception applies to electrostatic and electro-magnetic
fields of force, and for current conductors the planes normal to the
direction of the current are equipotential surfaces.

The contour of an equipotential surface of a field of force which is
drawn or represented by delineations of its lines of force can be
obtained by drawing a line normal thereto. This line will ordinarily be
more or less curved, and will be a locus of identical potentials.

An electric equipotential surface may be described as electro-static,
electro- magnetic, or magnetic; or may be an equipotential surface of a
current conductor. Besides these there are mechanical and physical
equipotential surfaces, such as those of gravitation.