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Amperes Law conceptual confusion.

  1. Feb 21, 2013 #1
    For amperes law it is stated that:

    ∫Bdl=μIenc


    My confusion is that B is that for example here now on earth if I have a compass. It interacts with a the magnetic field of the earth and points north. There is no I-enclosed yet there is still a magnetic field?


    Also another Amperes Law question involving a toroid:

    Outside of a toroid it is stated that the magnetic field is 0 because Ienc is 0. Can you not enclose current if your amperian path is larger than the toroid itself?
     
  2. jcsd
  3. Feb 21, 2013 #2
    Ok I understand now for the toroid, how the current negates itself but am still having trouble understanding how there apparently there is no magnetic field with no Ienc (with the compass question).
     
  4. Feb 22, 2013 #3
    I think that in the earth magnetic field question, you have a magnetic field which you don't care how was created.
    You have a small dipole, your compass.
    The dipole moment of the compass tends to allign with the terrestial magnetic field and thus points north.
     
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