About behavior of electrostatic pendulum near conducting or dielectric plate

The interaction of an electrostatic pendulum with a grounded conducting plate or a dielectric plate has been examined experimentally and theoretically. The force of interaction of a charged ball (an element of the pendulum) with its image in a plate was measured in equilibrium position. It was found that in both cases, for the same set of system parameters, the pendulum can have two stable equilibria. Calculation of the pendulum potential energy has shown that at certain values of the system parameters the potential energy can have two local minima corresponding to the two stable equilibria. A numerical simulation of an equation of bistable pendulum motion at external parametric force showed possibility of chaotic oscillations of the pendulum.