Flick a switch and get instant power—how our ancestors would have loved electric motors! You can find them in everything from electric trains to remote-controlled cars—and you might be surprised how common they are. How many electric motors are there in the room with you right now? There are probably two in your computer for starters, one spinning your hard drive around and another one powering the cooling fan. If you’re sitting in a bedroom, you’ll find motors in hair dryers and many toys; in the bathroom, they’re in extractor fans, and electric shavers; in the kitchen, motors are in just about every appliance from clothes washing machines and dishwashers to coffee grinders, microwaves, and electric can openers. Electric motors have proved themselves to be among the greatest inventions of all time. Let’s pull some apart and find out how they work!

The basic idea of an electric motor is really simple: you put electricity into it at one end and an axle (metal rod) rotates at the other end giving you the power to drive a machine of some kind. How does this work in practice? Exactly how do your convert electricity into movement? To find the answer to that, we have to go back in time almost 200 years.

Suppose you take a length of ordinary wire, make it into a big loop, and lay it between the poles of a powerful, permanent horseshoe magnet. Now if you connect the two ends of the wire to a battery, the wire will jump up briefly. It’s amazing when you see this for the first time. It’s just like magic! But there’s a perfectly scientific explanation. When an electric current starts to creep along a wire, it creates a magnetic field all around it. If you place the wire near a permanent magnet, this temporary magnetic field interacts with the permanent magnet’s field. You’ll know that two magnets placed near one another either attract or repel. In the same way, the temporary magnetism around the wire attracts or repels the permanent magnetism from the magnet, and that’s what causes the wire to jump.

The link between electricity, magnetism, and movement was originally discovered in 1820 by French physicist André-Marie Ampère (1775–1867) and it’s the basic science behind a Ac motor. But if we want to turn this amazing scientific discovery into a more practical bit of technology to power our electric mowers and toothbrushes, we’ve got to take it a little bit further. The inventors who did that were Englishmen Michael Faraday (1791–1867) and William Sturgeon (1783–1850) and American Joseph Henry (1797–1878). Here’s how they arrived at their brilliant invention.

Suppose we bend our wire into a squarish, U-shaped loop so there are effectively two parallel wires running through the magnetic field. One of them takes the electric current away from us through the wire and the other one brings the current back again. Because the current flows in opposite directions in the wires, Fleming’s Left-Hand Rule tells us the two wires will move in opposite directions. In other words, when we switch on the electricity, one of the wires will move upward and the other will move downward.

If the coil of wire could carry on moving like this, it would rotate continuously—and we’d be well on the way to making an electric motor. But that can’t happen with our present setup: the wires will quickly tangle up. Not only that, but if the coil could rotate far enough, something else would happen. Once the coil reached the vertical position, it would flip over, so the electric current would be flowing through it the opposite way. Now the forces on each side of the coil would reverse. Instead of rotating continuously in the same direction, it would move back in the direction it had just come! Imagine an electric train with a motor like this: it would keep shuffling back and forward on the spot without ever actually going anywhere.

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