Electric motor in ten minutes

You don’t always need a big laboratory for exciting experiments... For example, you could build an electric motor in just ten minutes.

Where would we be without the washing machine, iPod or electric toothbrush? Without the Toyota Prius, the vacuum cleaner and the refrigerator, or the power jigsaw, the escalator and the aquarium pump? In prehistoric times; that’s where we would be.

The discovery of the electric motor, which can convert electric energy into movement, changed the world, and not only because all manner of unpleasant tasks, such as climbing stairs or doing the dishes, suddenly became much easier. Without the electric motor the phenomenon of electricity would never have become popular with the public. It would have remained mildly amusing to make a filament light up, or a gherkin (see Episode 9), but to build an entire electricity network just for that...

The electric motor in its most primitive form was invented by the British physicist Michael Faraday. His invention consisted of a free-hanging strand of copper wire in a basin of mercury with a magnet in the middle of it. The wire would start to spin around when electric current ran through it.

Faraday’s set-up is a so-called homopolar motor. With a reasonably strong magnet, a battery and approximately twenty centimetres of solid-core copper wire you can build a similar motor in about ten minutes. As standard household magnets do not conduct electricity, you may also need a small plate of metal. You can also use a liquid conductor as Faraday did. Instead of using mercury (dangerous, unhealthy and illegal), use water with a few spoons of salt.

For the experiment in the Cogito ergo boom! lab we used a neodymium magnet. This has two advantages: neodymium magnets conduct electricity and they are very strong. Ridiculously strong. We have to admit we used a stack of four magnets instead of just one, the reason being we simply could not pull them apart!

Strip the insulation from the copper wire and make a coil. Bend the topmost end of the wire so that it touches the battery’s positive pole. The bottom end must touch the magnet or the metal plate. It requires a bit of finicking to get a good contact between the bottom of the coil and the magnet without the whole set-up falling apart. We solved this in the lab by using a thin piece of electric wire as a sliding contact on the magnet.

Place the battery on the magnet and place the coil over the battery. If you have done it correctly the copper wire will start to turn. Why does it turn? The electric current causes a magnetic field to be created around the wire. There is also a magnetic field surrounding the battery and the magnet. To put it simply, these fields push each other away, which is what causes the coil to move.

An electric clock works in the same way, but then the other way around. Using a quartz crystal and electronic components, exactly one pulse per second is sent through a fixed wire coil. The magnetic field around the coil gives a small magnet next to the coil a push every second. A small cog attached to the magnet sets the rest of the mechanism in motion. Tip for nerdy home tinkerers: the pulse generator in a clock has a 100% dependable fixed frequency of 1 Hz, making it very useful for all manner of experiments. If you use your imagination you’re sure to find a use for the electromagnet and the cogs too. As for the clock housing – throw it away, it's useless.

You do not necessarily have to bend the copper wire into a coil. We did an experiment with the wire bent into a heart shape, which worked too. It did cost a bit more effort to keep the whole set-up nicely in balance, though.

Author: Ernst Arbouw