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Poynting vector in static electromagnetic field

  1. Oct 21, 2010 #1

    zql

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    There is a situation, we have an electric field and a magnetic field, both are static. And we know the density of energy is u=E·D/2+B·H/2, so dU/dt=0, but Poynting vector S=ExH is not zero, which means energy is flowing. This confused me. Static field also has energy flux?
     
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  3. Oct 21, 2010 #2

    DrDu

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    Yes, correct. Look also for "hidden momentum".
     
  4. Oct 21, 2010 #3

    zql

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    can you give me more details?thanks.
     
  5. Oct 22, 2010 #4

    clem

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    The static magnetic field is produced by a constant electric current. That means there is resistance, and energy is flowing into matter. "Hidden" momentum is not involved.
     
  6. Oct 22, 2010 #5

    Andy Resnick

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    The relevant expression, from the conservation of energy, is:

    [tex]\frac{\partial u}{\partial t} + \nabla \bullet S = -J \bullet E[/tex].

    Does this help?
     
  7. Oct 22, 2010 #6

    zql

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    I think I got it, thanks.
     
  8. Oct 22, 2010 #7

    zql

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    And how about "hidden momentum"? I didn't know about this.
     
  9. Oct 22, 2010 #8

    DrDu

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    Probably the best source on these matters is still Jackson's book on Electrodynamics.
     
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