A magnet moving near a coil on a C-core

Class practical

In this experiment the coil of the wire is wound on a soft iron core and a permanent magnet is moved relative to it.

Apparatus and Materials

For each student group

• Copper wire, insulated with bare ends, 200 cm
• C-core, laminated iron
• Permanent bar magnet
• Galvanometer, sensitive to e.g. 3.5–0–3.5 mA., 10 ohm resistance (see note below)

Please note: Strictly speaking, we generate e.m.f. but frequently measure the current through the load resistor (i.e. the wire) using a galvanometer (not an ammeter).

Health & Safety and Technical Notes

Read our standard health & safety guidance

Procedure

1. Wind a coil of roughly 20 turns on one arm of a C-core.
2. Connect the coil by long leads to a galvanometer.
3. Place a magnet across the ends of the core. Observe the effect.

4. Remove the magnet. Again observe the effect.
5. Find out how the deflection on the galvanometer changes if the core is removed from the coil.
6. Investigate the factors which affect the deflection on the galvanometer.

Teaching Notes

Students will find that:

• There is only a current when the coil and magnet are moving relative to each other;
• Faster movement results in a bigger deflection;
• The iron core increases the size of the current;
• The current changes direction when the magnet moves towards and away from the coil.

This experiment was safety-tested in December 2004