An E&M Topic Presentation by Zach Levine

 Equipotential lines and surfaces are like contour lines on a map – except instead of altitude they represent electric potential, or voltage!  Electric potential is the electromagnetic equivalent of potential energy. It is measured in volts (V), which are joules per coulomb. 1 V = 1 J/C.  If matter travels along an equipotential line or surface, they experience no change in potential – hence the name “equipotential”.  Such lines and surfaces are the locus of all points that share a certain difference in potential from a charge.

In this diagram, the black charge in the center is positive, with the E-field radiating out of it. The rings around it are all equipotential lines; any point on a ring will have the same potential as any other point.

 Movement along an equipotential line or surface requires no work! This makes sense because work is proportional to the change in potential, and since the movement is always perpendicular to the electric field.  The direction of greatest potential increase, the gradient, is always perpendicular to the equipotential line or surface.  Equipotential lines and surfaces can exist in many different realms; from capacitors to point charges to dipoles. Each example is shown in the following slide, with the dashed lines representing equipotential.

 - a nice software for visualizing equipotential surfaces.  – a very useful lecture on the subject. There is a second part, in the “Related Videos” section.  - Wikipedia has accurate articles, if short, for anything.  astr.gsu.edu/hbase/electric/equipot.html - A very good website and the source of many of the diagrams here. astr.gsu.edu/hbase/electric/equipot.html