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I am reviewing my electromagnetism studies and I became confused with where energy of induced emf due to Faraday/Lenz' law come from.

Suppose that there is a curved track that starts with some height above loop of wires. The path passes through the center of the loop at the lowest point of the track. The track is symmetrical and it also ends at the same height as the starting height.

Now the bar magnet is placed at the starting point. As there is gravitation potential energy converted to kinetic energy, magnetic flux through the loop will change causing an induced emf. But this suggests that by conservation of energy, this electrical energy must have come from somewhere. Otherwise, we would be able to create electrical energy forever using a bar magnet. This is how my confusion arises. Where does the energy come from?

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See this one physics.stackexchange.com/questions/29569/loop-of-wire-in-a-varying-magnetic-fie‌​ld/29572#29572 –  KvdLingen Mar 20 '14 at 20:00

2 Answers 2

Look at the link provided. But the short answer is, it come from the kinetic energy of the magnet.

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Magnet or the loop - whichever is being moved :) –  tpb261 May 21 '14 at 6:16

There is no energy wasted/spent in the generation of a voltage across an open-circuited coil by any method (be it from another coil fed with alternating current or a bar magnet falling through coils). That's the simple theory.

In reality, induction will produce a short-lived voltage in the "receiver" coil and because there is self-capacitance in the coil (between windings etc.) a small circulating current will flow through the non-zero electrical resistance of the coil. This will dissipate a small amount of heat and slightly slow the magnet falling thru the loop of wire. Practically speaking it will be a very small transfer of energy.

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There is no mention of an open loop in the question. The loop may be open or closed. The answer should address both cases. –  Tobias Mar 21 '14 at 8:25

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