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Faraday's law states that Induced EMF is equal to rate of change of magnet flux linkage. Magnetic flux linkage is equal to the product of number of turns, area, and magnetic flux density. So EMF can be induced by changing the area, or magnetic flux density. I can understand that changing the area means moving electrons, which generate magnetic fields that interact with other magnetic fields to produce EMF. What I don't understand is how does changing magnetic flux density also produce EMF?? Take a transformer as an example: Alternating Current n the primary coil produces changing magnetic flux density. The area remains constant. Then how does it induce EMF?

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Faraday's induction law, that the EMF is proportional to the negative time derivative of the magnetic flux, actually describes two different effects which can be described by the same law. The first effect is based on the flux change due to the change of area of a conducting loop. In this case, the EMF is a purely magnetic force, the magnetic Lorentz force on the moving charge carriers in the conducting loop. The second effect is the induction of an electric field according to the Maxwell-Faraday equation of Maxwell's equations by a changing magnetic flux in a (not necessarily conducting) loop that is not moving relative to the magnetic field . It is, indeed, surprising that both effects can be described by the same induction law.

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  • $\begingroup$ It's indeed surprising that these 2 apparently different effects are the same--until you remember special relativity and covariance--which is why they must be the same. $\endgroup$ – JEB Mar 3 '18 at 20:25
  • $\begingroup$ @JEB- You are, of course, right! The relativity of the induction effect was also one of Einstein's observations that led to his Special Theory of Relativity. $\endgroup$ – freecharly Mar 3 '18 at 21:31

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