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A changing magnetic field induces an electric current in a coil. If you cross a magnet through the coil it will induce a current, but if the magnet is at rest relative to the coil there will be no current.

My question is if both the coil and the magnet inside it are on a rotating surface, will there be an electric current? After all, even if the distance between the coil and the magnet does not change, both will have different tangent speeds (assuming that the magnet is not a point in the center that would be at rest).

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  • $\begingroup$ Are the magnet and the coil moving with respect to one another, and is your rotating surface uniform (i.e. no slots, bumps, whatever)? $\endgroup$
    – TimWescott
    Jan 24, 2023 at 20:31
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    $\begingroup$ The only way you're going to generate electricity is if the coil sees a changing magnetic field. If your surface is ferromagnetic, then it will change (redirect) the field lines of the magnet. If your surface is ferromagnetic and non-uniform (e.g., has slots, bumps, holes as suggested by TimWescott) then the way in which it redirects the field lines will change as the surface rotates, and it potentially could cause the coil to see a changing field. Doesn't sound like a practical way to build a generator, but yeah, it's a possible way. $\endgroup$ Jan 24, 2023 at 22:32
  • $\begingroup$ Re, "...both will have different tangent speeds..." That means nothing. If the coil is at rest with respect to the magnet, then the coil is at rest with respect to the magnet. Period. End of story. The fact that there happens to be a rotating disk nearby does not change that relationship. $\endgroup$ Jan 24, 2023 at 22:39

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