Hi, I have been told that you take say a metal board and another board (both endless and paralell) leads to the following effect: The electrons are more or less freel in motion, they move to the surface until we reach an equilibrium. The electrons are assembled at the surface. Nice. Next lesson: Internally there is no electrical field. It holds: div(rho)=0 because rho is 0. Okay, rho is zero when the electrons are missing at the other side of the board... This counts only for the volume but not the surface!? Do I get something trivial wrong or is there a deeper reason? Thanks!