Veritasium's new video on electromagnetic levitation states that a rotating ring of magnets induce current in a conductor, which in turn creates a magnetic field.

He then says that this induced magnetic field is actually ahead of the rotation of the ring of magnets.

How is this possible?

Source: https://youtu.be/pCON4zfMzjU?t=3m56s


1 Answer 1


It is Lenz's law in action.
The induced currents will be in such a direction as to produce a magnetic field to oppose the motion the motion producing them.
In this case the magnets are rotating and that rotation is producing the induced current in the copper plate.
So the induced current produces a magnetic field to oppose the rotation which is an induced pole of the same polarity in "front" of the rotating magnet.

  • $\begingroup$ Thank you for your answer! Why couldn't the copper plate produce an attractive magnetic field lagging behind the rotatiin though? This would still oppose rotation, but would kill the levitation. Why does it levitate? $\endgroup$ Feb 3, 2017 at 15:16
  • $\begingroup$ If the plate was free it would be pushed forward to try to reduce the relative speed between the magnets and the plate. It levitates because the induced current produces forces to try and move the rotating magnets as far away as possible. $\endgroup$
    – Farcher
    Feb 3, 2017 at 22:41
  • $\begingroup$ Oh! So the induced current tries to produce magnetic fields to oppose the change in flux. This scenario of rotating magnets increases flux, so induced currents produce a magnetic field to decrease flux. If the plate was further away, the flux would be less. The plate can't move, so the contraption moves further, and levitates. That's wonderful! $\endgroup$ Feb 4, 2017 at 2:38

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