Magnets You Can Switch Off
- Physics
- Ages 11–14 · Grades 6–8
- Hands-on experiment
What you’ll find out
- An electric current makes a magnetic field around a wire.
- A coil around an iron core makes a much stronger magnet, which switches off with the current.
- More turns and more current make a stronger electromagnet.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Current makes a magnetic field
In 1820, a teacher named Hans Christian Ørsted noticed that a compass needle moved whenever he switched on a nearby circuit. Electricity makes a magnetic field around the wire. One straight wire makes only a weak field, so we wind the wire into a coil, where the loops add up and make it much stronger. Put an iron nail inside the coil and it is stronger still, because iron concentrates the field. This is an electromagnet. Switch the current off and it stops being a magnet.
Making it stronger, and using it
An electromagnet can be made stronger in two easy ways: add more turns of wire, or send a bigger current through it. You can measure the strength by counting the paper clips it will pick up. Ten turns might lift three clips, while forty turns lift about twelve. Electromagnets are everywhere. A scrapyard crane lifts a whole car and then drops it by switching off the current. Doorbells, electric motors and loudspeakers all contain them, and so do the machines that pull steel cans out of rubbish for recycling.
Curriculum links: NGSS MS-PS2-3 · NGSS MS-PS2-5