PHYS102: Introduction to Electromagnetism

Faraday's Law always involves loops that enclose a certain magnetic flux. If the loop is a conductor, then a changing magnetic flux creates a current inside the loop – even though there is no battery at all, and even if the wire has some resistance. This sounds contradictory because Ohm's Law says that you cannot have a current without a voltage; how can you have a voltage if there is no battery?

The changing magnetic flux itself acts like a battery, and the voltage it generates is therefore also called electromotive force (emf), just as for "regular" batteries. In other words, we have got a new type of power source for our electric circuits: the changing magnetic field is able to do work on the electrons inside the conducting loop, and if that loop contains a light bulb, you could make it light up, too. That is a transfer of energy which must come from somewhere.

From the electron's point of view, that energy comes from the magnetic field. But ultimately, work must have been done somewhere else to create the changing magnetic field in the first place. The law of energy conservation is never violated in this process.

Watch this video to explore different factors in Faraday's Law – the law that tells us how large the generated emf will be, depending on the rate at which the magnetic flux changes.