# Charges on outer surface only for conductors or all charged bodies?

## Main Question or Discussion Point

I read that charge resides on the outer surface of a charged (electrically) body. Is it meant only for charged conductors or all charged bodies including conductors or insulators? What are the specific points with respect to conductors and charges other than (i) conductors allow current freely (ii) conductors have no tangentical electric fiedl intensity E vector (iii) Conductors can not be charged by friction.

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Dale
Mentor
For (ii) I would probably say "there is no E field inside the conductor and the E field at the surface of the conductor is normal to the surface"

that charge resides on the outer surface
It's for conductors. The electrons all tend to repel each other. Moving to the surface is the only way they can get as far from each other as possible. In a conductor, they are free to move. In an insurator, the electrons have much less ability to move. In an insulator, the charges are usually on the surface because you probably caused the separation of charge to occur at the surface, i.e., you rub the fur against the glass rod -- that's the outer surface of the fur rubbing against the outer surface of the glass rod. The charge sits there because it's an insulator. But a metal is different - the electrons can travel to the surface.

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(iii) Conductors can not be charged by friction.
Is that right? I didn't know that. I would like to hear more about that.

Dale
Mentor
Even for the charges on the surface a conductor behaves differently from an insulator. On a conductor any surface charges will move away from each other in order to spread out as much as possible. But charges on an insulator are stuck where they are and cannot move away from each other. This allows both a tangential E field at the surface and an E field within the insulator.

Yes, conductors can not be charged by friction. Please refer discussion on this point in this forum itself - raised by me earlier.

Now, can insulators be charged by induction and can they be charged by conduction?

Dale
Mentor
Now, can insulators be charged by induction and can they be charged by conduction?
I don't think they can be charged by induction, but I do think they can be polarized by induction.

Any time anything is charged it is conduction (movement of charges) by definition.

Charging by conduction means transferring charge by touching. This does not happen in insulators. That is why we isolate charged conductors by covering them with insulators. In experiments, we hold the charged conductors/metals through insulator materials such as a plastic thread and wooden table.