Electromagnetism

The idea

A current in a wire produces a magnetic field around it, in circles around the wire. The field is stronger with a bigger current and closer to the wire. Shaping a wire into a coil (a solenoid) increases the strength of the field; inside a solenoid the field is strong and uniform. Adding an iron core makes an electromagnet, which can be switched on and off.

1. Describe the field shape around the wire or solenoid.
2. List ways to increase the strength.
3. Give a use of an electromagnet.

Watch out An electromagnet's field disappears when the current stops; a permanent magnet's does not.