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Repulsion between two electrons

Discussion in 'Electronic Design' started by ~~SciGirl~~, May 19, 2005.

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  1. ~~SciGirl~~

    ~~SciGirl~~ Guest

    Ok, say there are 2 electrons, repelling each other.
    There are photons between them, and the repulsion is caused by the photon's
    "kick", right?
    \ /
    \ e- / e-
    \ ??? /
    ~ ~ ~ ~ ~ ~
    / \
    / e- \ e-
    / \

    So that's the basic Feynman diagram, missing some parts and labels but as
    much as I can do on the computer I think.

    My question: what frequency is the photon that causes the repulsion?
    According to uncertainty, it should change depending on how close to each
    other the electrons are, right??? So if they were far enough away, it would
    be maybe the wavelength of a radio wave, and if they were really close
    together, an x-ray? And if so, if we put them the right distance away from
    each other, could we get visible light?

    ---------- That was the first part ------------

    Now the second part. Say there's an electron and a positron attracting each
    other. (I'm not going to make the diagram for that, it's too hard with just
    the slash marks and stuff). How do the two particles attract? Some opposite
    of "kick"? And could we vary the frequency of the photons there too?

    ***Before you criticize someone, walk a mile in their shoes. That way,
    you'll be a mile away and you'll have their shoes***
    Sci~Girl the Obsessive
  2. Rich Grise

    Rich Grise Guest

    No. There is only a force between the two electrons. When they _move_,
    it's the force times the motion that "causes" a photon. I've modified
    your diagram a bit here:
    A photon is the medium of energy exchange. When they're just sitting
    there, there is force, but no motion, so no energy is transferred.
    Another word for this force is "voltage". It's simply pressure, that
    isn't doing anything yet.
    Close enough, if I understand what you're asking, not that I know what
    a "Feynman diagram" is. I guess I could look it up, but I think it would
    only confuse the issue - oh, all right....
    Oh! You've got electrons moving, and "bouncing off" each other. I
    thought your diagram was just two electrons sitting there. So I was
    the one who was confused. but I'm too lazy to start over, so I'll just
    correct myself as I go along.

    So, yes, when moving electrons bounce off each other, there is
    acceleration. There's motion, the electron's motion, and there's
    force, which is the repulsive force (EMF in my modified _stationary_
    diagram above), and force * motion = work, which is very much like

    So the frequency (wavelength) of the photon depends on how fast
    the electrons are moving, and how close they get - how energetic the
    collision is.
    That depends on the amount of energy moved from one place to the other.
    When an electron moves a large distance but not with a lot of force, that
    will create a long photon, like from an antenna. When it moves a very
    short distance, but with huge amounts of force, then you get X-rays,
    like off the anode of an X-ray tube.

    And yes, in between, there's visible light - I'm pretty sure that's
    how an xcimer laser works. There's also synchrotron radiation, which
    is what you get from electrons that are moving along a curved path -
    the combination of their charge, and the acceleration results in
    work, or energy, which escapes as photons.
    Again, it's simply electromotive force, the same way a balloon can stick
    to your hair. But their movement, in combination with that force, will
    release energy. ---- OK, first time through, I was seeing them just
    sitting there attracting each other. But an electron and positron won't
    bounce off each other - depending on how close to head-on they come,
    they'll either swing around in hyperbolic orbits, and the acceleration
    releases a photon, or if they're dead-on, they'll annihilate.
    When the electron and positron actually do crash together, they're
    completely turned into a photon - that's a gamma ray. If they just
    swing around each other, it depends on how fast and how close they

    Hope This Helps!
  3. Except you're taking it literally by assuming that it's a point
    event because that's what the diagram seems to show. It isn't,
    because the diagram is an extremely simplified form of shorthand
    notation for a fairly complicated process.
    The electromagnetic force extends to infinity, so the electrons
    are continually exchanging photons no matter how far apart they are.
    There's no specific frequency to nail down unless the electrons are
    bound into physical matter as opposed to being in vacuum. In matter,
    the presence of the fields associated with other charges places
    restrictions on the frequencies of the photons they can exchange.
    "Bound" can also mean being within a cavity resonator like a magnetron.
    In vacuum, similar to above except the force is attractive.

    Until somebody finds/invents Dilithium, we don't really have to
    worry about the bound condition. The cavity situation is exemplified
    in particle/antiparticle colliders.

    You really ought to post questions like this in
    sci.physics.electromag, you know.

    Mark L. Fergerson
  4. The photons are "virtual" photons. Lookup "solitons" and "dark solitons"
    for insight.

    You may find this helpful:



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