1. The problem statement, all variables and given/known data Context: Between the two conducting cylinders of a coaxial cables, there is a dielectric hollow cylinder. There is free static charge Q on a length L of the inner conductor, and free static charge -Q on a length L of the outer conductor. Upon calculating that the polarisation field P = K/(ρ) (where the constant K accounts for charge, permittivity etc.. and ρ is the variable distance from the center). We are then asked to find the bound volume charge density within the dielectric. 2. Relevant equations -div (P) = ρb 3. The attempt at a solution Upon calculating the divergence, I find ρb = 0 . This is confirmed by the solutions manual. But I don't understand how this can be possible. The P field lines aren't closed lines as far as I know (unlike B field lines). They source at bound negative charges and sink at bound positive charges. How can there be a P field if there is no polarisation charge density spawning it? Please tell me if any of the assumptions I make above are wrong. Also, I suspect this might have something to do with distinguishing between surface and volume polarisation charges, but I don't see how that changes things.