In 1820 a Danish professor, Hans Christian Ørsted, noticed during a lecture that a compass needle jumped when he switched on a current in a nearby wire. Electricity can make magnetism!
Key idea
A coil of wire with electricity flowing through it is a magnet, an electromagnet. Wrap it around an iron nail and it gets stronger. Switch off the current and it stops being a magnet.
| Make it stronger | Why |
|---|---|
| More turns of wire | each turn adds to the magnet |
| More current (a stronger battery) | more flow, more magnetism |
| An iron core (a nail) | the iron becomes a magnet too |
Electromagnets are in doorbells, speakers, cranes that lift scrap cars, and electric motors. A motor uses electromagnets pushing and pulling on magnets to make something spin: a fan, a mixer, a toy car.
Worked example: Why use one?
A scrapyard crane lifts a car, moves it and drops it in a pile. Why use an electromagnet instead of a regular magnet?
- A regular magnet cannot be switched off.
- An electromagnet lets go the moment the current stops.
Answer: So it can drop the car when the current is switched off.
Common mistake
Thinking an electromagnet stays magnetic forever. It is a magnet only while the current flows (a steel nail may keep a little magnetism).
Look and listen
- Hold a compass near a running electric fan or hair dryer (do not open them). Does the needle move?
- Look for motors around the house: anything that spins when you switch it on.
Going further. Michael Faraday turned this idea into the first motor and generator: Faraday: Experimental Researches in Electricity. Later: Electromagnets in Physical Science.