Solenoid and Electromagnet

A coil that turns magnetism on and off.

A solenoid is a long coil of wire. Inside it the field is nearly uniform, and from outside it looks like a bar magnet. The field gets stronger with more turns per metre, more current, and a soft iron core placed inside.

Unlike a permanent magnet, an electromagnet can be switched off, which is why it is used in cranes that lift scrap, in electric bells and in relays.

• Soft iron concentrates the field and loses magnetism easily.
• Reverse the current to swap the poles.
• Strength depends on turns, current and the core.

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