Lenz's law

Where does the energy come from which lights the bulb. It must come from the work we have to do when we push the magnet into the coil.

The emf induced in the coil produces a current if we have a circuit, which we do in this case. This current will produce a magnetic field and this field opposes the motion of the magnet, forcing us to do work when we insert it. On the diagram above, when the magnet is removed from the coil the induced field would try to stop the magnet being removed by attracting it.

Another way of thinking about this is to remember that when you cut flux you have to do work.

An induced emf will always oppose or try to oppose the flux change causing it.

The coil is connected to an a.c. supply. The aluminium ring floats up the iron retort stand. Emf's are induced in the ring and these produce eddy currents in the ring. The field produced by these currents opposes the changing field causing them, so the ring floats.	The iron core of a transformer is laminated (made of slices of iron glued together). If not then large currents would be induced in the core and it would get very hot, making the transformer inefficient.	This is an induction motor. The opposition of the two fields (from the stator and in the coil) makes the coil rotate.