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Electrons and positrons free fall within a superconducting cylinder

  1. Feb 6, 2009 #1
    I read about electrons and positrons free fall within a superconducting cylinder, in this book (p 105):


    I don't understand what I read.

    Apparently, electrons would feel an electric field mg/e that would actually freeze them in the cyclinder. This is already not totally clear. But I assume that any motion would create huge reacting currents in the cylinder to balance the motion. This would be the usual Lenz law. But I would like to that understand better.

    Where I really don't understand is when positrons are discussed.
    Apparently they would feel a -mg/e field that would in total result in a 2g acceleration. I feel this is very strange since this is contradictory to my usual understanding of the Lenz law: the induced current would then re-inforced the motion instead of damping it.

    Any suggestion ?

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Feb 6, 2009 #2
    WIthout further details one can only speculate But it sounds like an electric field (E) is set up in which case the magnitude of the electric force on both the electron and positron would be the same(Ee).In the case of the electron Ee acts up to balance its weight
    (mg=Ee) and for the positron Ee acts down making a resultant force(mg+Ee=2mg).
    This reminds me of Millikans experiment where e was measured.
  4. Feb 6, 2009 #3

    It seems that a field appears spontaneaously.
    This is not totally surprising.
    What is surprising if the effect on positrons.
    I would expect the same effect both for e- and p+, since the effect should actually counter-act on the motion of the particle.

    Here is what I don't fully understand:


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