The electrostatic problem of a point charge inside a capacitor made of two parallel grounded electrodes is illustrated in this Demonstration The electric potential and field can be calculated as an infinite sum of image charges On the left you see the space between the two parallel plates represented by horizontal red lines Move the point charge and view the resulting electric field blue streamlines and equipotential lines black On the right you can see the set of real and image charges red for positive blue for negative as well as the location of the two real plates solid red lines and several of their images dashed gray lines