An electromagnet is a device whose invention has sparked a worldwide technological revolution. They’re now found in almost every device from your phone to your loudspeakers to your car; and they’re also found in larger forms in hospital magnetic resonance imagers and particle accelerators. But exactly how is it that electromagnets work? Let’s take a look.
When electric current flows through a wire, it generates a small magnetic field around it. The protons in the wire are all oriented in the same direction, and thus they exert magnetic force on the surrounding particles. We can amplify this force by forcing the current to run in a coil shape. The more frequent the coils, and the stronger the current, the stronger the magnetic force will be.
Wrap the coiled with around an iron core, and you’ll have effectively made a permanent magnet. The only difference is that this particular magnet can be turned on and off again at the moment’s notice.
Electromagnets of this sort are especially important when controlling high-current circuitry. It might be difficult or unsafe to turn such circuitry off and on using a simple mechanical switch, or you might wish for the circuit to be switched on and off automatically based on the incoming current. By using a circuit with a lower current to actuate a magnet, it’s possible to safely activate and deactivate a circuit without endangering life and limb.
The coils of wire which comprise an electromagnet can be arranged in several different ways. In a straight wire, the field will appear in rings around the wire as the current flows around it. In the case of a flat coil of wire, they’ll be an array of rings, with the space in the centre carrying electromagnetic force in a given direction.
The most useful sorts of electromagnets, however, are the solenoid spirals we’ve discussed. The magnetic field is created within and around the solenoid, allowing it to charge any length of magnetic material (like an iron nail) that’s inside it.
An electric motor, like the starter motor you’ll find in a car, isn’t just activated using an electromagnet. It also takes advantage of magnetic principles to generate spin. A coil of wire is place in between two magnetic poles. When the current flows through, the ends of the poles are drawn toward their opposite numbers. By flipping the magnet on and off rapidly, and changing the polarity every time, it’s possible to continually pull the central shaft around and around.
As well as causing a wheel to spin, it’s possible to use magnets to draw energy from a wheel that’s already spinning. This is how the turbines at a hydroelectric power facility work, using motion from the water to actuate magnets which in turn generate electricity. It’s also how the battery in your car is charged via an alternator, which uses the motion of the crankshaft to charge the battery as the car is in motion – thereby ensuring that you don’t ever run out of juice.
Inductors work by passing a magnet through a coil of wire in order to induce a current in the complete circuit. The faster the magnet moves, and the stronger it is, the more charge will be generated.
Where else might an electromagnet be used?
Electromagnets are famously used in speakers. Alongside a permanent magnet set just behind the driver cone, they’re able to move the cone backwards and forward. This produces changes in air pressure which we hear as sound. A microphone works in much the same way, but in reverse: a mobile magnet will be moved backwards and forwards near a fixed one, which in turn generates a current that can be later recorded and then turned into sound.
An MRI machine at your local hospital also makes use of electromagnets. It bombards the hydrogen atoms in your body with magnetism, causing them to align in a certain way, and then emit radiation as the magnet is turned off, which the detectors in the interior of the machine are able to interpret and turn into the image itself. This technology allows doctors to see the interior of your body and make complex diagnoses with little risk. It’s helped to save and improve countless lives since it was first conceived of.