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If we place a bar magnet along the x axis, the magnetic field near its poles would be parallel to the x axis. Now, let's bring a circular loop near the the magnet, moving the loop along the x axis. Notice that the electrons in the loop are then moving parallel to the magnetic field, so there should be no force on them and hence no current. But Lenz's law says that there will be an induced current. Where have I gone wrong?

  1. Is is because the magnetic field near the poles is not exactly parallel to the x axis?
  2. Or is there some other force moving the electrons and thus creating a current?

I found this question but I'm afraid I understood none of the answers except the one by Holger Fielder, which I understood to some extent only.

Anurag Baundwal
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1 Answers1

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It's option 1: the magnetic field near the poles is not exactly parallel to the $x$-axis for a bar magnet. Rather, there is a component perpendicular to the axis as well, and this causes a tangential Lorentz force on the charges.

Here's another way to think about it: Suppose that the magnetic field lines were exactly parallel to the $x$-axis. Then the loop would be moving parallel to the field lines at all times. This means that the flux through the loop would not be changing, and thus Faraday's Law ($\mathcal{E} = - d\Phi/dt$) would predict no EMF induced in the loop.

Michael Seifert
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