What is electromagnetic induction ? Describe an experiment with a coil, a bar magnet and a galvanometer to demonstrate it.

Answer: When the magnetic field linked with a coil (conductor) changes, a potential difference and hence a current is induced in the coil. This is electromagnetic induction.

Experiment: Wind a coil of insulated copper wire with many turns and connect its two ends to a galvanometer G. (Diagram to draw: a cylindrical coil, its ends joined to a galvanometer; a bar magnet with N and S marked held along the axis of the coil, with an arrow showing it being pushed into the coil.)

1. Push the north pole of the bar magnet quickly towards (into) the coil: the galvanometer needle deflects, say to the right. A current is induced.
2. Hold the magnet still inside the coil: there is no deflection, because the magnetic field linked with the coil is not changing.
3. Pull the magnet away from the coil: the needle deflects in the opposite direction (to the left).
4. The faster the magnet is moved, the larger the deflection. The same results are obtained if the magnet is kept fixed and the coil is moved.

Conclusion: A current is induced in the coil only while the magnetic field through it is changing. This principle was discovered by Michael Faraday and is used in the electric generator.