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I have a doubt about electromagnetic induction, in three particular cases. I need to confirm that I have the right concepts, so I ask for your help.

The main problem:

Imagine that you have a permanent magnet, axially polarized and rotating on its axis with a constant angular speed. Surrounding this magnet, a coil (constant area section pointing in the same direction of magnet polarization). The main question is: will there be induced voltage?

This is what I think:

1) We know that, for a constant Area, flux linkage ψ = B*A*cos θ.

In this case θ = 0°, so ψ = B*A.

And the induced voltage is ε = -N*dψ/dt = -N*A*dB/dt.

In this main case, I think that there will be no variation in B, because the rotation does not change it at all. So dB/dt = 0, thus ε = 0.

2) Let's suppose the magnet is now radially polarized, but keeping the surrounding coil. In this case, can I affirm that rotation still doesn't change B at all (actually it does change B, but if we consider the whole thing it does not)? And not only because of this ε is zero, but θ = 90°, which implies ψ = 0.

3) Now suppose the coil doesn't fully surround the magnet. Let's say it covers only 270° of it (a little abstraction is needed, I know :tongue:). In this case of non-symmetry, there will be a variation in B, but ε is still zero because θ = 90°.

Am I correct? Did I miss something?

Thank you,

Marcus

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# Electromagnetic Induction

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