Electric Current: what is it?

  • #1

Main Question or Discussion Point

I have a question which is driving me nuts. I have, in all probability, got the wrong end of the stick somewhere, and if so I would be really grateful if someone could pinpoint my confusion.

One reads in introductory Physics books that an electric current IS moving electrons.

But I have also read that the speed of movement of electrons in a DC circuit is rather slow, yet the current moves very quickly indeed.

In an AC circuit there is, apparently, no net directional movement of electrons. Furthermore
the electricity company don't send electrons out through your wall socket.

So, it seems to me, moving electrons can't be the current, all they can be is the facilitators of current. The analogy that strikes me is that of a wave moving across the ocean, water molecules are able to move about which enables the wave to pass through them, but there is little (if any) net directional movement in water molecules despite the very fast speeds encountered in phenomena such as Tsunamis.

Is this all hopelessly muddled? If not then what exactly is electrical current?

Answers and Replies

  • #2
Think of a chain on a bicycle. Think of electrons as being each link in the chain.

Now with the bike upside down you can slightly move the chain back and forth and the wheel will turn. The chain links near the crank stay near the crank and the ones over at the rear wheel stay near their area. You are not sending chain links over to the rear wheel but it is turning.

(When you pedal backwards on most bikes it does not put any force on the wheel so the force is all in one direction)

This is exactly how an AC current works, the electrons only move very slightly back and forth on the wire, but the force is transfered through them just like links on a chain.
  • #3
Staff Emeritus
Science Advisor
Like Lost said above, the electrons are moving back and forth along the entire grid. Each individual electron doesn't move very far, but they are all moving like links in a chain.
  • #4
Much like a pipe filled with water, a conductor is filled with electrons. No matter how long, adding electrons (or water) to one end will almost instantaneously result in all the electrons/ water moving through the pipe and coming out the other end.

The actual water or electrons don't move that fast, but the "push" does.

So indeed, putting a battery to a circuit will result in an almost immediate motion of all the electrons in that circuit (no matter how long the wire is) without them necessarily having to move fast or far.
  • #5
Science Advisor
Gold Member
I think it is easy to lose sight of the fact that there are in the region of 1023 movable electrons in just a few grams of a metal. You can get an enormous flow of net charge (i.e current) if each one moves only a couple of mm per second.

Life was a lot easier when they just told you about Current, Volts and Resistance and you could accept the results of the calculations. The fact is that Electrons are not necessary for the understanding of most of electrical theory. It was largely sorted out long before Chadwick actually spotted an Electron!!!

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