Electromagnets: field pattern

Class practical

Exploring the magnetic field pattern for a C-core.

Apparatus and Materials

For each student group

• Copper wire, PVC-covered, 150 cm with bare ends
• C-core, laminated iron
• Cardboard

• Iron filings in a pepper pot

• Plotting compass

• Power supply, low-voltage

Health & Safety and Technical Notes

Warn the class to keep fingers away from eyes. Iron filings inadvertently carried to the eyes can damage the cornea.

Read our standard health & safety guidance

Procedure

1. Take an iron C-core, place a card on top, and sprinkle with iron filings. Is there any magnetic field pattern? Test with a plotting compass.
2. Wind twenty turns of PVC-covered copper wire round one arm. Connect it to the DC terminals of the low-voltage power supply.
3. Switch on, and investigate the magnetic field produced. Identify N and S poles.

Teaching Notes

• There is no field pattern around the C-cores until a current passes through the coil wrapped round the C-core.
• A compass needle will indicate that the two ends of the C-core have opposite magnetic poles.

This experiment was safety-tested in July 2007