If you place a conductor in an external E-field the charges inside it will move so as to cancel off the field making the field inside the conductor zero. My question is: Is this also true if you place some net charge on a conductor? Will the field inside it then still be zero? The net charge will flow to the surface yes, but will it also be true that the charges are able to cancel off the field produced by the net charge? And why is it that net charge always resides on the surface of a conductor. You could say I suppose that it always minimizes the mutual potential energy between the point charges originating from the net charge, but don't you have to take into account how the positive and negative charges from the conductor itself position themselves?