Method of image charges

Summary

The method of image charges solves electrostatic boundary value problems by placing fictitious charges outside the region of interest. The fictitious charges are chosen so that the total potential meets the boundary condition, such as zero potential on a grounded conductor. The uniqueness theorem for Poisson's equation then shows that this potential is the true one inside the region. It gives closed formulas for the Green's function of a half-space and of a ball.