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Grades 8–10 Intermediate About 20 min Version 1 Awaiting review Premium

Build an electromagnet

A current in a wire makes a magnetic field. Winding the wire into a coil (a solenoid) adds up the fields of all the turns, so the coil behaves like a bar magnet with N and S poles. Putting a soft iron core inside makes the field hundreds of times stronger, because the iron becomes magnetised too. This is an electromagnet. Unlike a permanent magnet, it can be switched on and off and its strength can be changed by changing the current or the number of turns.

What you will learn

  • Build an electromagnet and test its strength.
  • Describe the effect of the number of turns, the current and the core.
  • Give uses of electromagnets.

Before you start

  • Know that a current-carrying wire has a magnetic field.

Materials

  • Insulated copper wire, a large iron nail, a plastic straw and paper clips

Equipment

  • Low-voltage power supply with an ammeter and a switch

Procedure

  1. With an iron core and 1 A, count the clips lifted with 20, 40 and 80 turns.
  2. With 40 turns, change the current to 0.5 A and 2 A.
  3. Replace the iron nail with a plastic straw (air core) and compare.
  4. Switch the current off and see what happens.

How this simulation is simplified

  • Each paper clip needs the same pull; the field is proportional to turns × current.
  • The soft iron core makes the field 20 times stronger than an air core.