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TOPIC 11:    Electromagnetism and Electromagnetic Induction

Tip 1:

When a loop of wire moves about in a uniform magnetic field, with its plane perpendicular to the field, no current is induced in the coil.  Why?

According to Faraday's Law, an e.m.f is induced only if there is a change in magnetic flux linkage.  Since the coil is always in the field, its magnetic flux linkage is unchanged hence no e.m.f is induced.

But didn't we learn that when a wire cuts the magnetic flux, an e.m.f will be induced? where E = Blv sin q.

This apparent contradiction can be explained as follows:

Imagine that the loop of wire is rectangular.

As the loop moves from left to right, an e.m.f will be induced in the side AB, with A at a higher potential than B; an e.m.f will also be induced in the side CD, with D at a higher potential than C.  Applying Kirchhoff's Voltage Law, there is no net e.m.f around the loop (i.e. the potential differences cancel out), hence no current can flow.

This is consistent with Faraday's Law: since there is no change in magnetic flux linkage, there is no net e.m.f induced in the loop.

 

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