State Lenz's law. Explain, by giving examples, that Lenz's law is a consequence of conservation of energy.
Solution
Lenz's law: the direction of an induced current is always such that it opposes the change in magnetic flux that produces it. Example — a magnet pushed towards a coil: the near face of the coil develops a like pole and repels the magnet, so the person must do work to push it in. This mechanical work is exactly the source of the electrical energy that appears as the induced current. If the induced current instead aided the motion, the magnet would accelerate on its own and produce electrical energy at the same time — energy would be created from nothing. Since that is impossible, the induced current must oppose the change. Hence Lenz's law is a direct statement of the conservation of energy.
