Luke Thelin, of Henley Primary School, asks :-

How fast does electricity travel through a wire?

John Campbell, a condensed matter physicist at the University of Canterbury, responded.

There are several possible answers to this question depending on what you are using the electrical wire for.

If you are using it for signalling or communications then the signal travels just outside the wire at an incredibly fast speed. Light and wireless waves travel through space and air at about three hundred million metres every second. Such signals take about five thousandths of a second to travel the length of New Zealand, a bit over a tenth of a second around the world and over eight minutes to travel from the Sun to the Earth. (The sun could have vanished seven minutes ago and we wouldn't know about it. Scary eh!) If the wires are immersed in plastic, such as in the round aerial cable to your TV set, these signals slow down to two hundred million metres every second. That's real fast.

Metals conduct electricity because a small piece of the atom, the electron, is available to move through the wire leaving the atom behind. When a current is switched into a wire a metre long the first electron comes out the far end about fifty millionths of a second later.

At any instant one of these electrons can be travelling at about one hundred thousand metres every second. Thats pretty fast. However the electron doesn't travel very far before rebounding after smacking into some sort of impurity in the copper wire, such as a vibrating atom or an impurity atom such as oxygen. The conducting electron therefore drifts only very slowly down the wire. If we look at a particular electron entering a copper wire that is one meter long, one millimetre in diameter and carrying one ampere of electrical current then it will take that particular electron nearly three hours before it emerges from the other end. That's real slowwwww.