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Magnetic fields qustions

  1. Jul 28, 2003 #1


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    [SOLVED] Magnetic fields qustions

    I don't understand the correlation between the two following source of magnetic fields:

    1- Electric Dipole
    2- Moving Electron

    I can't build a concept that allows me to explain them both! Are they both caused by moving electrons? #2 is by definitions but #1? In a permanent magnet, is it the motion of electrons of many aligned dipoles (like a selenoid) that cause the magnetic field?
  2. jcsd
  3. Jul 28, 2003 #2
    I may be wrong, but i think its not so much the alignment of electrons but the spin. :shrug:
  4. Jul 31, 2003 #3
    on the source of magnetic fields

    I am under the impression that all magnetic fields are made by moving charges. Electrons orbiting in atoms make magnetic fields parallel to the axis of the orbit in addition to the field created by their spin. I'm not sure though how these combine to create or not the field of an atom. I guess a dipole would have a field too, but it depends on the releative angles of the axis' of the particles' spin.
  5. Jul 31, 2003 #4


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    An electric dipole consists of oppositely charged electric particles separated by a distance. There is no magnetic field associated with a dipole until it moves.

    An electron being a single negative charge is surrounded by an electric, like the dipole there is no magnetic field until something moves with respect to (wrt) the electron.

    A electric field changing wrt time(ie moving)generates a magnetic field, likewise a changing magnetic field generates an electric field.

    So to directly answer your question, a neither a dipole nor a electorn automatically generates a magnetic field, The magnetic field is generated by motion of a electric field.
  6. Jul 31, 2003 #5

    Now I'm no expert, but I'm pretty sure that electrons have a magnetic field as a result of their charge and spin. I thought that's what spintronics is all about, the manipulation of the direction of a electron's spin by using magnets to flip it one way or another.
  7. Jul 31, 2003 #6


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    Notwithstanding Jonathan's comment on spin, the electron is in constant orbital movement so it always moves so always generate a magnetic field. How else would you explain the magentic attraction between stationary atoms?

    What does "changing with respect to time" really means. Does it mean move or accelerate or change direction or intensity or rotate???
  8. Jul 31, 2003 #7
    I think he means in magnitude and/or direction, since those are the only ways for it to change.
  9. Jul 31, 2003 #8


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    A solitary electron is a single negitive charge, all spin effects are very small and negligable as far as a magnetic contribution.

    An atom is an intirely different topic of discussion. Once again, while each "orbiting" electron generates a magnetic field the sum of all contributions (ie electrons) is essentially zero except for a few special cases (iron can hold a premenate magnetic field). Atoms can be diamagnetic, paramagnetic or feromagnetic, this is according to how they react to an applied magnetic field.

    What I said in my original post is the fundamental physics you want to think about. This is the physics of Maxwell's equations which model the basic interaction of charges and electro magnetic fields.

    Coulomb's law says that a region containing an electric charge is the source of an electric field.

    Gauss's Law states that no region contains the END of a magnetic field line.

    Faradays law relates a space changing Electic field and a moving charge to a time chaning magnetic field.

    Orested law relates a space changing Magnetic field to a time changing Electic field.

    Together these four equations (which I discibed but did not state) constitue the four Maxwell equations. Do some research on them if you wish to understand electro magnetism.

    Edit: I had a major Typo in the last description. It now reads correctly!
    Last edited: Jul 31, 2003
  10. Jul 31, 2003 #9


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    Allright I get. Thx guys
  11. Jul 31, 2003 #10
    Integral is correct. An electron
    at rest is not generating a mag-
    netic field. However it is gen-
    erating an electric field which
    radiates out in all directions.
    Physically moving the electron,
    whether it be by pushing it
    through a conductor, or literally
    shifting the position of a charged
    piece of plexiglass causes a
    kink in that electric field be-
    cause the center of radiation of
    that field is now in a different
    position. It is these very kinks
    in the electric field that are
    the electromagnetic field.It's
    that simple.

  12. Jul 31, 2003 #11
    I disagree. An electron has spin and charge and so it has an unchangable and ever existent magnetic field!
  13. Jul 31, 2003 #12


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    You are quibbling over a 2nd order effect. Once again the self magnetism of an electron is very small, it is the source of the Zeeman effect this is observed as spectral line splitting in an applied magnetic field.

    It is not a significant factor in major electro magnetic effects.
  14. Aug 1, 2003 #13


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    That's a very good visual Zoob. Could I rephrase this by saying that the magentic field is effectively a result of a spatial imbalance in the electric field (ie. moving the charge in one direction has the effect of "superimposing" the electric field in the direction of the movement)?
  15. Aug 1, 2003 #14

    I'm glad it conjured up an image
    for you.

    I don't feel qualified to give the
    O.K. to your proposed paraphrase
    because I'm not sure that what
    is happening falls into the cat-
    agory of a superimposition. It
    may, in fact, be more to the
    point to visualize it as a com-
    pression of the lines of force
    of the electric field.

    It was the discovery of this "kink
    in the electric field" in an
    encyclopedia, that finally allowed
    me to pull everything in the EM
    spectrum together in my mind.
    Before this I didn't have a clue
    how artificially produced radio
    frequencies belonged together
    with visible light, for example.

    Is "spatial imbalance" a better
    term than "kink"? I wish I knew
    enough to say yes or no.

  16. Aug 1, 2003 #15


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    A changing electric field (as might be created by wiggling a charge) creates a changing magnetic field. Similarly, a changing magnetic field creates a changing electric field.

    - Warren
  17. Aug 1, 2003 #16

    Question on that phenomenon:

    Where do I look for the wiggling
    magnetic field in a stationary
    charged object? Do the charges
    "seethe" around, in and on it?

  18. Aug 1, 2003 #17


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    The wiggling magnetic field around a stationary charge? What the hell are you talking about?

    - Warren
  19. Aug 1, 2003 #18
    Thank you, Warren.
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