Chapter 3 Method of Images: Example 3.2+Problem 3.7
Consider a system with two charges q and q’. In order to use the method of images, we need to determine if we can find a position to put charge q’ such that the boundary conditions are satisfied.
The electrostatic potential and field generated by this system of two point charges outside the sphere will be the same as the potential and field generated by the point charge and the sphere.