State Faraday's laws and Lenz's law of electromagnetic induction. Show that Lenz's law follows from the law of conservation of energy.

1. 1 · State Faraday's laws. An emf is induced whenever the flux linked with a circuit changes; its size equals the rate of change of flux: ε = −N dφ/dt.
2. 2 · State Lenz's law. The induced current flows so as to oppose the change that produces it.
3. 3 · Draw the set-up. [Bar magnet with N facing a coil joined to a galvanometer; an arrow for the magnet's motion; the near face of the coil marked N with an anticlockwise current arrow]
4. 4 · Apply it. As the N pole approaches, the near face becomes N and repels the magnet; as it moves away, the face becomes S and attracts it.
5. 5 · Bring in energy. Work must be done against this opposing force; it appears as electrical energy and then as heat in the coil.
6. 6 · Rule out the other case. If the current helped the motion, energy would be created from nothing, which is impossible.
7. 7 · Link to life. This is why a generator gets harder to turn when more lamps are switched on.
8. 8 · Close in one line. So, Lenz's law is the law of conservation of energy applied to induced currents.

Scoring tip: Use the word 'oppose' and say what is opposed: the change in flux, not the flux itself.