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Let's consider a permanent magnet and a coil. No current flows through the coil. Can the permanent magnet induce an EMF into the coil (and thus an induced current)? Why? Many thanks.

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  • $\begingroup$ Hint: A changing magnetic field induces an electric field. $\endgroup$
    – sbp
    Nov 17 '17 at 20:22
  • $\begingroup$ @sbp Yes, for sure. But why can a magnet with remanent magnetization considered as a changing magnetic field? Magnetization is a property of a 'magnetized' ferromagnetic material related to the magnetic field measured inside the material... what could I misunderstand? Thanks! $\endgroup$
    – sunrise
    Nov 17 '17 at 21:08
  • $\begingroup$ Okay. It's not about a ferromagnetic material having a changing magnetic field. The field is constant for such a material. Say I fix the loop. Now I bring in the magnet from far away. So for the loop there was initially no $B$, but as I bring the magnet closer there is a changing $B$ that the loop feels, there is a change in flux, and thus current flows in the loop. Infact the current flows in such a direction so as the abhor this change in $B$. This is called Lenzs Law. Look up Griffiths. $\endgroup$
    – sbp
    Nov 18 '17 at 3:35
  • $\begingroup$ @sbp Ok, if some movements are allowed, everything is clear. But in a device like this one physics.stackexchange.com/questions/369212/…, where permanent magnet and coil are attatched, I have to conclude that the current induced by the permanent magnet was induced at the beginning of the assembly process.. Is it correct? Thanks again! $\endgroup$
    – sunrise
    Nov 21 '17 at 16:59
  • $\begingroup$ See the point is that $\textbf{B}$ should change with time to induce $\textbf{E}$ and viceversa. $\endgroup$
    – sbp
    Nov 21 '17 at 20:01
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A permanent magnet will only induce a current if it in motion relative to the coil.

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  • $\begingroup$ Ok, but in this case the coil and the permanent magnet are attatched... I think that the explanation is in the condition "permanent magnet with remanent magnetization" $\endgroup$
    – sunrise
    Nov 17 '17 at 21:14
  • $\begingroup$ If the coil and permanent magnet are attached I see no way in which a current could be induced, the motion has to be relative. $\endgroup$
    – LUPHYS
    Sep 19 '18 at 1:23
  • $\begingroup$ current can be induced if u change the reluctance, by inserting a ferromagnetic core in the coil for ex $\endgroup$ Sep 19 '18 at 2:30

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