Physics / Unit 10: Magnetism and Modern Physics
10.2 Electromagnets
Notes
A current in a wire makes a magnetic field around it (discovered by Oersted).
- Around a straight wire, the field forms circles. Right-hand rule: thumb along the current, fingers curl in the direction of the field.
- A coil of wire (solenoid) carrying current acts like a bar magnet.
- An electromagnet is a solenoid wrapped around an iron core. It can be switched on and off.
- Make it stronger by increasing the current, adding more turns of wire, or using an iron core.
- Uses: scrapyard cranes, doorbells, speakers, MRI machines, relays.
Practice
Which change would make an electromagnet weaker?
Less current gives a weaker magnetic field.
What is the main advantage of an electromagnet over a permanent magnet in a scrapyard crane?
Switching off the current removes the magnetic field.
A compass is placed next to a wire. When a large current is switched on in the wire, the compass needle moves. This shows that:
This is Oersted's discovery linking electricity and magnetism.
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