Is the net charge on conducting wire positive, zero or negative when current flows
through it?
Answers
For electric currents inside a real-world conductor, with some real ohms of resistance, there must always be a voltage distributed along the conductor, and a proportional gradient of surface charge associated with this voltage.
So, for a simplified conductor, one end must have a positive net-charge, and the other end has a negative net-charge, with zero charge in the center. If the wire has both uniform diameter and conductivity, then the charge is distributed smoothly from one end to the other.
On the other hand, if the conductor is part of a circuit, then the above charge-distribution will be summed with an overall average charge (as when a positive wire with zero current has a net positive charge.) The “slope in charge” must always be there during a current, but it’s usually combined with a non-zero net charge common to that whole piece of wire.
All of the above is separate from another issue: what polarity do the particles have, as they flow during electric currents? This question is best answered by looking at liquid conductors, such as long hoses full of salt water. The water-hoses may have the surface-charges described above, but also they’re full of charged sodium and chlorine atoms (ions.) During a current, the sodiums go one way and the chlorides the other, like clouds passing through each other. But on average, the charge down inside the salt water is zero. For “charged” conductors, the net-charge is only on the surface. Down inside any conductor, the *average charge* is zero, but also this “uncharged” charge flows during an electric current. (For every positive sodium, there is a negative chloride nearby which cancels it out. But whenever they move in opposite directions, that’s a charge flow …even though the average charge inside the material is zero!)