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Homework Help: Light's magnetic fields

  1. Jun 17, 2012 #1
    1. The problem statement, all variables and given/known data

    This is just a conceptual question that I've been personally wondering about. So light has a magnetic field wave perpendicular to an electric field wave. I don't quite understand the magnetic field wave though.

    I thought that magnetic fields were not supposed to have a beginning or end. They continuously travel in a loop from north pole to south pole. How then does light's magnetic fields work? Where are the north and south poles and where are the loops? How is it that the diagrams just depict linear magnetic field vectors?

    Diagram example: http://www.google.com/imgres?um=1&h...=195&start=0&ndsp=15&ved=1t:429,r:8,s:0,i:164

    I have googled this to a great extent but have not been able to find an answer.

    Any help would be greatly appreciated. Thanks.
    Last edited: Jun 17, 2012
  2. jcsd
  3. Jun 18, 2012 #2


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  4. Jun 18, 2012 #3
    Thanks for the reply ehild.

    I know that the light wave is self propagating with its changes in electric flux and magnetic flux.

    My question, however, is that in an EM wave are the magnetic field lines also something like concentric circles like that of around a current carrying wire? Or are they really just straight lines pointing in one direction?
  5. Jun 18, 2012 #4


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    The are like concentric circles around the changing electric field lines, which are circles around the magnetic field lines.


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  6. Jun 18, 2012 #5
    They are not rings but more like flattened ellipses.
  7. Jun 19, 2012 #6
    horizontally is time, so these aren't loops in space like magnetic field line loops.
  8. Jun 19, 2012 #7
    horizontally is time, so these aren't loops in space like magnetic field line loops.
  9. Jun 19, 2012 #8
    BTW i only did the one post, are multiple repeat postings a common bug on PF?

    (as you can see the system knows they are both my third post, but has them logged at different times!)
  10. Jun 22, 2012 #9


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    it happens sometimes! :smile:

    i think it's when you click "Submit Reply" but nothing happens, so you click again :wink:
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