Making a permanent magnet

Class practical

Using a current-carrying coil of wire to make a permanent magnet from a steel rod.

Apparatus and Materials

• Copper wire, PVC-covered, 150 cm with bare ends
• Rod, hard steel

• Iron filings in a pepper pot

• Tintacks or paper clips, supply of
• De-magnetizing coil (300 turns or 2400 turns)
• Transformer or low-voltage AC supply

• Power supply, low-voltage

Health & Safety and Technical Notes

Read our standard health & safety guidance

The steel rod may be a knitting needle or a piece of clock spring. As a poor substitute, short pieces of thick piano wire can be used.

Make sure the hard steel samples are not magnetized. If any are, de-magnetize them by passing them slowly through a coil carrying AC: for the 300-turn coil, use about 6 V AC: for the 2,400-turn coil, use about 20 V AC.

Procedure

1. Use iron filings or a plotting compass to check that the steel rod is not magnetised before proceeding
2. Wind a few dozen turns of insulated wire around the steel rod. (Leave enough wire free at either end to make connections to the power supply.)
3. Connect the ends of the wire to the low-voltage DC power supply, so that a large current flows round the coil.
4. Switch off the current. Test the steel rod again to see if it has become magnetised.
5. Determine where the rod's magnetic poles are.
6. Devise a method for magnetising the rod in the other direction.

Teaching Notes

• How Science Works Extension: Students can make a magnet (by this method, or by the stroking method) and then test its strength. This requires them to devise and evaluate an approach to measuring the strength of a magnet. Here are some suggestions:
• Find how many pins, tacks or paper clips will hang end-to-end from the magnet.
• Lay a pin on the table. Gradually bring the magnet towards it. Measure the distance at which the pin starts to move.
• Place a plotting compass on the table. Bring the magnet towards it from the side (east or west). Measure the distance at which the compass needle points at 45° to its original direction.
• Students should be able to think of other ideas. By trying out several, they can evaluate the sensitivity of each.

This experiment was safety-checked in July 2007