Three charged particles are shown in the animation along with their electric field and their electric potential. Double clicking in any location draws the equipotential surface through that location. You can click drag any of these particles. Holding the mouse down on any location shows the x and y position of that location and the potential,V in volts, at that location in a box at the bottom of the simulation.
Double click in several different locations on the screen to see more eqipotential surfaces. Move the charges around. What is the relationship between an equipotential surface and the electric field vectors at that location?