Magnetic fields due to arrangements of magnets

Class practical

Iron filings will align with the direction of a magnetic field to reveal the field pattern.

Apparatus and Materials

For each student group

• Permanent bar magnets, 2
• Magnadur magnets, 2
• Steel yoke
• Card

• Iron filings in a pepper pot

• Plotting compasses
• C-cores
• Aluminium rings

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

Permanent bar magnets are those bar-shaped magnets with opposite poles at either end. Magnadur magnets are ceramic magnets with their poles on their flat faces.

If iron filings get on the poles of a magnet, they can be removed by rolling Plasticine over the poles.

Procedure

1. Explore the area around a permanent bar magnet with the plotting compass, by moving the plotting compass around the magnet. Concentrate on the bar magnet and the space surrounding it, as well as the compass needle.
2. Sprinkle iron filings on a card and place the card over the magnet. Tap the card gently with a pencil and observe the pattern.
3. Repeat this using two magnets, first attracting, then repelling.
4. Instead of the permanent bar magnets, use two Magnadur magnets. Again investigate the field using:
5. iron filings sprinkled on card
6. the plotting compass
7. The Magnadur magnets can be put on the bench as shown, or attached to the iron yoke.

Teaching Notes

Students will see that the iron filings tend to concentrate close to the magnetic poles of the magnet.

This experiment was safety-tested in December 2004