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Homework Help: Magnets sliding down metal sheets (slower then non metals)

  1. Jul 14, 2010 #1
    hey guys, ive been given an assignment on the topic of eddy currents and magnetic induction. We have been given info that when a magnet slides down an incline over a magnetic sheet, the eddy currents in the metal acts as a braking mechanism (lenz's law).

    I've done some research and what i dont get is how why there is eddy currents involved when there is no voltage or emf being put into the metal sheets??

    Also why does factors such as different metals, thickness affect the speed of the magnet sliding down??

    thanks in advance.
  2. jcsd
  3. Jul 14, 2010 #2


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    The sliding magnet plus metal sheet act like a dynamo ( very rough example). the magnets motion is transformed into electrical current, and that slows the magnet as it looses energy.

    The path of the eddy currents is complex, have fun!!!
  4. Aug 1, 2010 #3
    the basic ideas is that, the change in magnetic flux through a closed "loop" induces an emf in it. In your case u say that the magnet slides over a magnetic sheet, which means that there is a change in flux through any arbitrary loop drawn at the surface of the magnetic sheet upon which the magnet slides.
    so that's it.. definitely an emf will be induced and u can expect eddy current to flow, if the sheet is a good conductor. The current flowing would tend to brake the magnet, because as u have already mentioned, by lenz's law u can say that the current induced would tend to stop the change in magnetic flux, so it will tend to stop the magnet and hence brake it.
    I hope now u can quite well figure out why the speed of the magnet will be different for different sheets. That's because the conductivity of the sheet will determine the amount of eddy current that will flow, in the sheet. A sheet will greater conductivity, will let more current flow so the "brake" to ur magnet would be applied much earlier in case of a good conducting sheet as compared to some weaker conducting sheet.
    There's nothing to wonder much about it and as "Lok" already said, the path of eddy current is quite complex to draw! So u should rather not try to trace the path of eddy currents too much as they might really confuse u!!!!
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