All wires get a little bit hot when they’ve got a current running through them, because as the electrons move in the wire they bang into the metal atoms. And whenever they prang into an atom, energy from the moving electrons gets given off as heat.
We use copper for electrical wiring because it’s easy peasy for electrons to move around in, so not too much energy gets wasted as heat. But if it’s heat you want, say for your hairdryer/toaster/electric jug, it’s dead easy to get. You just need to use a bit of metal that’s really hard for electrons to move through, like nickel.
Heating elements like the ones in toasters or hairdryers are bits of wire made of a nickel/chromium alloy called nichrome. Run a current through nichrome and you’ll get some serious heat. While the electrons in the copper wires can move around easily, the ones in the nichrome element are constantly banging into the nickel and chromium atoms and leaking heat all over the place. Which is just what you want on those wet-haired, stale bread days.
But heating is only one of the things electric appliances can do. Most of the other things involve making things move – and that involves a motor. So how do organised electrons make a motor spin?
Every electron is like a tiny, weak magnet. Most electrons hang around in pairs, and they cancel each other’s magnetic property out. But some materials — like iron — have got some unpaired electrons around their atoms. And if you can get those unpaired electrons to line up so their magnetic fields are all pointing in the same direction, your piece of iron is suddenly a magnet. Which is exactly what happens when you stroke a needle or paperclip with a magnet — the magnetic field around your magnet pulls some of the unpaired electrons in the needle into lines, so all their mini-magnetism adds up to a full scale magnet.
But you can also make any metal into a temporary magnet — an electromagnet — just by running an electric current through it.
Electromagnets work because the charge on an electron can create a magnetic field too, but only when it’s moving. So any time electrons in a wire are moving in synch (ie whenever a current is flowing), the wire becomes a magnet. It’s too weak to be a useful magnet as it is. But if you coil the wire around a piece of iron, the weak magnetic field around the wire forces unpaired electrons in the iron to line up, and all their mini-magnetism adds up just like in a bar magnet.
But unlike a regular magnet, the wire is only magnetic while the current is flowing — once it stops, the electrons in the wire get back to acting like sub-atomic dodgems. And the piece of iron its wrapped around goes back to being a piece of iron.
And it’s the ability of an electric current to turn wires into temporary magnets that makes it possible for us to have motors that can be switched on and off.
If you’ve ever used one magnet to repel another, you already know the basics of how electric motors work. In fact, if you used the north end of one magnet to push the north end of another magnet around in a circle, you’d be doing pretty well the same thing an electric motor does. Except a motor doesn’t have a giant hand pushing one magnet to repel another — it relies on a set of magnets in a ring surrounding a loop of wire.