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Neutrons in electromagnetic fields

  1. Mar 20, 2015 #1
    Consider a moving neutron passing by an electromagnet, will a neutron be deflected? This video seem to show that the neutron would have to be charged in order for it to move
     
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  3. Mar 20, 2015 #2

    Simon Bridge

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    How? When?

    Note: Objects do not have to have a charge to be deflected by a magnet.
    http://www.phys.utk.edu/witek/np621/symmetrytests.pdf [Broken]
    ... see section on neutron spin: they are little magnets.
    ... directly after that, see the brute force measure for neutron neutrality.
     
    Last edited by a moderator: May 7, 2017
  4. Mar 20, 2015 #3
    The video implies that the neutron would have to be charged at 2:44 The proton in the video moves because it is electrostatically repelled by the length contracted Protons in the wire. A neutron, being neutral, cannot experience this force.
     
    Last edited by a moderator: May 7, 2017
  5. Mar 21, 2015 #4

    Simon Bridge

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    If a neutron were to experience the force being illustrated, then it would have to be charged. But there is nothing there to indicate that the neutron experiences the force being illustrated.

    Basically you are noticing that the video is incomplete.
    Did you read the link?
     
  6. Mar 21, 2015 #5
    "Objects do not have to have a charge to be deflected by a magnet." I was aware of this, I was just pointing out that the mechanism described in the video seems to imply that neutrons won't deflect, when they should, showing that the special relativity explanation is inconsistent with reality,
     
  7. Mar 21, 2015 #6

    Simon Bridge

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    ... or that the short introductory demo in a youtube video is somehow incomplete...

    BTW: what makes you think that neutrons deflect in the circumstances described in the video?
     
  8. Mar 21, 2015 #7
    I just thought so since they have magnetic moments,
     
  9. Mar 21, 2015 #8

    Simon Bridge

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    Work it out - would a neutron, in the situation that the video places a proton, be deflected by the magnetic field of the wire?
     
  10. Mar 21, 2015 #9
    I'l say no, however, it must be deflected by permanent magnets which work on a different principle
     
  11. Mar 21, 2015 #10

    Simon Bridge

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    Permanent magnets use electromagnetism just like electromagnets do.
    You cannot do physics by analogy - try using maths (or experiment).

    In the link I gave you it shows you that neutrons are not deflected by a uniform electric field - which would need to be the case for the circumstances in the video above to show a contradiction. A neutron can be deflected by a non-uniform magnetic field - as int he Stern-Gerlach experiment. The field about a wire is non-uniform in the direction the field points in - like it is in the S-G apparatus. That is not the case for the wire.

    You may want to get together with this person:
    https://www.physicsforums.com/threads/two-velocities-in-the-lorentz-law.804172/
    ... you are studying the same video. Perhaps you are in the same class?

    It will also benefit you to get other sources.
     
  12. Mar 21, 2015 #11
    "Permanent magnets use electromagnetism just like electromagnets do." This video seems to imply that it's the intrinsic magnetic moment rather than the effects of special relativity
     
  13. Mar 22, 2015 #12

    Dale

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    You have to be careful not to overgeneralize small concepts. In the video they are specifically discussing the magnetic force on a point charge outside a current carrying wire. They are not even talking about the magnetic field. The magnetic force can always be made zero by transforming to a frame where the point charge is at rest, but that does not imply that the magnetic field is zero nor does it imply that the force on a magnetic dipole could be made zero.
     
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