"When positive charges move in unintelligible directions, then per definition, we say the current goes in this direction. When negative charges go in this direction, we also say the current goes in that direction, that's just our convention. If I apply a potential difference over a conductor, then I'm going to create an electric field in that conductor. And the electrons -- there are free electrons in a conductor -- they can move, but the ions cannot move, because they are frozen into the solid, into the crystal.

And so when a current flows in a conductor, it's always the electrons that are responsible for the current. The electrons fuel the electric fields, and then the electrons try to make the electric field zero, but they can't succeed, because we keep the potential difference over the conductor..."