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When a magnet is moved into solenoid, it induces a current. And, when it is moved out of the solenoid, it induces a current. But what about in the example below. When a very long magnet, that has its whole body within the solenoid, is moved in some direction. The magnetic flux experienced by the coil from the magnet, should be very similar even if the magnet as a whole was moved a few centimeter.

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For the same oscillation of the magnet, The induced current tends to zero when the length tends to infinity. Because the magnetic field inside the coil is almost uniform in this case.

I assume the magnet with longitudinal displacement. The field is clearly no uniform transversely and a transverse movement would induce a current.

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  • $\begingroup$ how is that different in the case of the homopolar dynamo, see en.wikipedia.org/wiki/Homopolar_generator? $\endgroup$
    – hyportnex
    Commented May 19, 2023 at 21:51
  • $\begingroup$ @hyportnex Because the field is (almost) parallel to the motion. In the homopolar dynamo, the motion is perpendicular to the field. $\endgroup$
    – BowlOfRed
    Commented May 19, 2023 at 22:44
  • $\begingroup$ @BowlOfRed Exactly, $\mathbf v \times \mathbf B=0$, and this is missing from the answer but even then if there were current it would be almost perpendicular to $\mathbf B$, not so simple. $\endgroup$
    – hyportnex
    Commented May 19, 2023 at 22:47
  • $\begingroup$ @ClaudioSaspinski Hi I think I phrased the title misleading. It said "moved back and forth" but I was really just interested in movement overall. Since you wrote "oscillation of magnet" I assumed you assume it was moved back and forth. Will induced current still tend to zero if magnet is just moved in one direction? $\endgroup$
    – BipedalJoe
    Commented May 19, 2023 at 23:11
  • $\begingroup$ @BipedalJoe I edited the answer to clarify this point. $\endgroup$
    – Claudio Saspinski
    Commented May 20, 2023 at 13:02

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