How do electromagnets work?
Electromagnets work thanks to a fundamental force called electromagnetism. In the 19th Century, Hans Christian Ørsted noticed that a wire with a current running through it affected a nearby compass. The current was creating a magnetic field. Later research showed that electric current and magnetism are actually two aspects of the same force. This force works both ways – a moving magnetic field creates electric current. This is, in fact, how generators work.
The mechanism that actually causes electromagnetic force involves quantum physics and the transfer of photons, but the mechanics of an electromagnet are quite simple. All you need is a power source, a wire and a core. When a current passes through a wire, the resulting magnetic field takes the shape of concentric circles around the circumference of the wire. The magnetic field gets weaker farther from the wire. Coiling the wire makes for a much more efficient electromagnet, because inside the coil the magnetic fields of many portions of the wire are concentrated into a small space.
The coil is wrapped around the core, which should be made of a magnetically permeable material such as iron. The core itself is not magnetic under normal circumstances, since all the magnetic areas within it (known as magnetic domains) are pointing in different directions, cancelling each other out. When the current is turned on, the magnetic field generated by the coil of wire forces the magnetic domains to line up, which makes the core itself magnetic. The stronger the current, the stronger the magnetic field. This makes even more of the domains line up, increasing the overall strength of the electromagnet.
When the current is shut off, most core materials revert to a non-magnetic state as the domains flip back to the original positions. However, certain substances can become permanent magnets and retain the alignment of the magnetic domains even in the absence of current.
Electromagnets in action
1. Scrapyard magnetic cranes
Magnetic cranes in scrapyards turn on the powerful magnet to lift tons of metal, then turn it off to drop the scrap.
2. Recycling plants
In keeping with the scrapyard theme, electromagnets are used to separate certain metals from huge piles of unsorted scrap and waste.
The speakers in your stereo or guitar amplifier use electromagnets to convert electrical energy to sound waves – variations in the current make the magnets, and the speaker cones, vibrate.
4. Electric motors
Electromagnets, in combination with permanent magnets, are an integral part of electric motors, which are pretty much everywhere.
5. Particle colliders
Experimental devices such as the Large Hadron Collider use massive supercooled electromagnets to focus the particle beams.
Discover more amazing science in the latest issue of How It Works. It’s available from all good retailers, or you can order it online from the ImagineShop. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, make sure you subscribe today!