Describe the experiments of Faraday and Henry with a magnet and with two coils. What do they show about electromagnetic induction?

1. 1 · Define the effect. Electromagnetic induction: an emf is induced in a circuit whenever the magnetic flux linked with it changes.
2. 2 · Magnet and coil experiment.
   • Magnet pushed in: G deflects.
   • Magnet at rest: no deflection.
   • Magnet pulled out: opposite deflection; faster motion gives a larger deflection.
3. 3 · Draw the set-up. [Coil C₁ joined to galvanometer G; bar magnet with N facing the coil; arrow for the direction of motion]
4. 4 · Two-coil experiment. Pressing or releasing the key in C₂ gives a momentary deflection in C₁; a steady current gives none; a soft iron core increases it.
5. 5 · Real life. Generators in power stations use the same effect to make electricity.
6. 6 · Close in one line. Therefore, only a changing magnetic flux, by relative motion or by a changing current, induces an emf.

Scoring tip: Always say what happens when the magnet is held still: examiners look for 'no change in flux, so no emf'.