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Magnet in a copper tube

  1. Feb 1, 2012 #1
    1. The problem statement, all variables and given/known data
    If I drop a magnet through a long tube of copper how would the EMF vary with time?

    2. Relevant equations



    3. The attempt at a solution
    When the magnet enters the copper tube some of the magnetic flux lines are being cut hence an EMF is induced in the copper coil
    If we look at flemmings left hand rule how does this work. We have a force downward and lets say the south end of the magnet is at the bottom, the magnetic field lines point downwards. So where does the force act?

    Now when half the magnet is in the coil and half not apparently the EMF is at a maximum, why?

    Also, apparantly, when the magnet is in the tube no EMF is induced. BUT when we carry out experiments it would suggest this is NOT true as it takes longer for a magnet to fall through the tube than a non-magnetic item (by a significant amount of time!). What is the real answer?

    I do know that the induced voltage would be greater when the magnet falls through the other end as its moving faster so the rate of change of flux linkage is greater hence EMF induced is greater

    Could someone please help fill in the gaps and possible either walk me through what happens or tell me what happens

    Thanks :)
     
  2. jcsd
  3. Feb 1, 2012 #2
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