# How does electric field propogate in a wire? [duplicate]

When I say electric field, I'm referring to the electric field that causes the movement of charge in the wire.

I have learnt about currents and resistances, but I have never really had an understanding of how the voltage across a conductor actually causes current to flow.

Well there must be an electric field to cause the motion of the charges, and there must be some mechanism by which the electric field is set up in the wire.

It must be some sort of chain reaction, because we know that the electric field changes direction as the wire changes direction. And it must be quick as we know from practical experience.

So how is the electric field set up in the wire? Could it have something to do with instantaneous accumulation of charge?

p.s: I'm a highschool student and I'm only looking for an intuition.

Take, a battery. It has many negative charges gathered at one pole. They repel each other strongly, since they all produce a negative electric field.

If you connect a wire to this pole, then suddenly the charges feel a neighbour location with less repulsion. Imagine being the charge at the edge of the charge bundle, feeling a lot of electric repulsion force from the bundle, and now suddenly a path opens up next to you with less repulsion. This charge will immediately move to this path.

Where that charge came from is now an empty space with less repulsion for all the other charges. So, another charge will immediately take over this spot. This means that the first charge that moved now again feels a repulsion from behind, and it thus moves further ahead.

All other charges feel the same less repulsion on this wire-path. They all want to move there. They will thus "queue" up to move along this path. The charge in front is moving due to the push from the electric field of the charge behind it. And that charge moves forward due to the electric field of the charge behind that one.

Eventually, the entire circuit is filled up with charges.

Note: This is a simplified picture, since there area already charge in balance filling up the wire. The repulsion is still less along this path, so negative charges form the battery pole will indeed push on the charges that are already along the wire. They will then in turn push their neighbour charges - and this is propagation of the "push" happens at the speed of light.

The repulsion force is an electric force. A larger electric force is what we associate with a larger electric potential energy. On a per-charge basis we call it simply electric potential. Whenever you have two points with not the same repulsion against a charge, then that means two points at different electric potentials.

A difference in potential is what we call voltage. So, there we have it: Voltage is just a word for a difference in electric repulsion; a word for a charge's tendency or willingness to move to that other point. The voltage thus describes the "pressure" that makes charges flow throughout any circuit.

• Thanks for replying. So if I understood correctly, if suppose you consider an arbitrary part in the wire, there is a charge imbalance for a very short time which causes an electric field which pushes the electron forward so as to nullify this charge imbalance? And this electron which was pushed further creates a charge imbalance and this goes on as a chain reaction? – Michael Faraday May 9 at 21:03
• Also, why does this propogation happen at the speed of light? The propogation involves the movement of electrons, and the speed of electrons in a conductor is relatively slow. So shouldn't the propogation be related to the speed of electrons? – Michael Faraday May 9 at 21:04
• @MichaelFaraday Yes, you understood correctly. Regarding the electron speed, an electron is slow like a single soldier in a marching platoon is slow. But when the first guy calls out, the signal can quickly move to the last guy. The slow motion of electrons which you are referring to might be the drift velocity, but with a closely pack electron network on the material, any disturbance at one point quickly propagates to the other due to the very fast random motion of electrons which causes them to very quickly interact with their neighbours. – Steeven May 9 at 21:17
• Thanks a lot @Steeven! – Michael Faraday May 10 at 6:24