1. The problem statement, all variables and given/known data A solid metal cylinder of radius R and length L, carrying a charge Q, is surrounded by a thick coaxial metal shell of inner radius a and outer radius b. The shell carries no net charge. Find the potential at the center, using r=b as the reference point. 2. Relevant equations V= (1/4πεo)q/r V = -∫E dot dl 3. The attempt at a solution The cylinder is not infinite but I assume I'd have to ignore end effects. I want to approach this problem using gauss's law to find the field and then integrating. I don't even think I can use the first equation since my reference point is not at infinity. This is easy enough but I'm having problems because I don't know the electric field at the boundaries. I can find the field easily when r<R when R < a < b and when a < r < b I don't know what the field is exactly at the surfaces?