A magnet moving near a coil on a C-core
Practical Activity for 14-16
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
- Wind a coil of roughly 20 turns on one arm of a C-core.
- Connect the coil by long leads to a galvanometer.
- Place a magnet across the ends of the core. Observe the effect.
- Remove the magnet. Again observe the effect.
- Find out how the deflection on the galvanometer changes if the core is removed from the coil.
- Investigate the factors which affect the deflection on the galvanometer.
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