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A maglev train is riding because the magnets in the train are reflecting their magnetic field on the aluminium rail, so it is lifted up. Also when you rotate a aluminium plate and you hold a magnet above it, it will reflects his own magnetic field (north or south)and is repeling it.

In a way you can compare it with looking in the mirror. You can see yourself because light is reflecting on the mirror back to you. But in case of a mirror you won't need any movement, but why is that in case of magnetic fields?

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  • $\begingroup$ Magnetic fields are electric fields which arise due motion due to decrease in effective distance. Given by $z= r\sqrt{1-\frac{v^2}{c^2}}$ $\endgroup$ – Anubhav Goel Feb 10 '16 at 10:11
  • $\begingroup$ A varying magnetic field induces eddy currents in aluminium materials. This currents induce magnetic field which weaken the external magnetic field. BTW, the higher the speed of the plate the higher the damping (or the force you need to move the plate). $\endgroup$ – HolgerFiedler Feb 10 '16 at 10:53
  • $\begingroup$ About eddy current I ask here physics.stackexchange.com/questions/234983/… $\endgroup$ – HolgerFiedler Feb 10 '16 at 11:08
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The point that you are missing is that light which is a type of electromagnetic wave consists of oscillating electric and magnetic fields. So your assertion is not correct. In the case of a metal the light causes the free electrons to oscillate and reradiate what you call the reflected light.

I am not sure about the use of the term reflection in the context of the maglev. If you move the north pole of a magnet towards a metal plate a force is produced on the free electrons which then move and so a current is produced. That induced (eddy) current produces the equivalent of a north pole which repels the incoming north pole. This process generate heat because a current is flowing in the aluminium which has resistance. If the aluminium is replaced by a superconductor the there is no energy loss and engineers think that this may in the future be the method to be use for magnetic levitation.

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  • $\begingroup$ I don't understand why that current produces also a north pole, Why creating something that is repelling yourself? And I thougt that only when the aluminium plate is rotating (or the magnet?) their is the same magnetic field produced/reflected, but I don't see that back in your answer. $\endgroup$ – Marijn Feb 10 '16 at 13:36
  • $\begingroup$ The reason it is a north pole is as a result of the law of conservation of energy. When the eddy current is produced and heat is generated where does that energy come from. It come from the work done in moving the north pole of the magnet against the repulsive force towards the north pole produced by the eddy current. If it had been a south pole produced then the poles would attract and with no work being done an eddy current and hence heat is produced. $\endgroup$ – Farcher Feb 10 '16 at 13:49
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Aluminum is diamagnetic, and conductive. So, an impinging magnetic field induces currents that repel the magnet, BUT electrical resistance in the aluminum dissipates energy and the current soon decays to zero. The current in the aluminum causes nearly perfect cancellation of the total field (due to the impinging magnet AND the electromagnet which is the internal current), at the aluminum surface, but that's not exactly reflection. The reason you need movement to see this in aluminum, is the decay of the induced current: if you replaced the aluminum with a superconductor, the current wouldn't decay. If you replaced the aluminum with a diamagnetic material which wasn't conductive, the repulsion might be very weak (but wouldn't decay).

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