Magnet and coil
An introduction to the dynamo principle.
Apparatus and materials
For each student group
Permanent bar magnet
Copper wire, insulated with bare ends, 200 cm
Health & Safety and Technical notes
a Wind a coil of 10 to 20 turns with long leads (say 50 cm). The coils should be such that a permanent bar magnet can pass freely through.
b Connect the long leads to the galvanometer.
c Move the magnet in the space in and around the coil, keeping an eye on the galvanometer. Summarize your observations.
1 You might introduce this experiment by saying:
A dynamo or generator is a carefully-designed piece of equipment. There is a coil of wire and a magnetic field. There is motion. Electricity (a voltage) is generated. You can understand the principle of the dynamo by starting with a simpler situation: you have a coil and a magnet, and you can move them. What will you discover?
2 The students should find out that:
- the current flows only when the magnet and the coil are moving relative to each other;
- the current changes direction when the magnet is inserted into the coil and then removed from the coil;
- more turns on the coil produce bigger currents provided the total length (i.e. the total resistance) of the wire remains the same;
- the faster the magnet is moved, the greater is the maximum deflection.
This experiment was saftey-checked in April 2006