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The Source of Proton Charge

  1. Sep 9, 2009 #1
    Electrons have no known substructure, right?
    ...And they have a negative charge.

    Protons have known substructures...and protons have a positive charge.
    From whence does the positive charge of a proton arise, if not from the charges of a proton's substructures per se (in the way an ion has a charge as per its charged substructures)?
  2. jcsd
  3. Sep 9, 2009 #2
    Hi there,

    This is one question that scientist are still trying to find. More precisely, the charge distribution of the proton is an experiment that I had the chance to work for back in the days. Therefore, a simple answer to your question would be very hard to give.

  4. Sep 9, 2009 #3


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    The charge of the proton does come from the charges of the quarks that it is comprised of: two up-quarks with charge +(2/3)e each, and one down-quark with charge -(1/3)e.
  5. Sep 9, 2009 #4
    Ah, thank you! And where do the quark's charges come from?
  6. Sep 9, 2009 #5
    It is the inclusive picture that gives you such a simplified notion of a point-like electron.
    In fact, any scattering from an electron is accompanied with soft radiation due to permanent coupling the electron to the quantized EMF. As soon as this coupling is permanent, the electron and the quantized EMF form a compound system with a smeared quantum mechanically charge distribution (somewhat similar to an atom). The elastic scattering cross section is the equal to zero, and all inelastic cross section with a finite number of final photons equal zero too. It is inelastic cross section which is observable. It corresponds to the average (summary) picture of all inlesatic processes. As any average, it is rather deterministic value that can be attributed to a free point-like particle with a Coulomb potential. So the latter is an approximate, inclusive picture, not primary one.

    The same reasoning is applicable to proton and its charge distribution.

    It is funny to note that the atomic orbitals manifest "partial" charge localization (somewhat similar to quarks):
    Last edited: Sep 9, 2009
  7. Sep 9, 2009 #6


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    The same place the electron's charge comes from: it is just a basic postulate that the leptons and the quarks come with certain electric charges.

    (Actually, it's slightly more involved once you take into account how electromagnetism fits into the Standard Model, but the Standard Model requires essentially equivalent postulates.)
  8. Sep 10, 2009 #7
    Isn't "charge" simply an intrinsic attribute, like mass or angular momentum? If my understanding of these concepts is correct, asking 'where does an electron get its charge' is like asking 'where does an electron get its angular momentum'. If we only knew....
  9. Sep 11, 2009 #8


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    You mean it`s spin, not angular momentum
  10. Sep 11, 2009 #9
    Yes, sorry. I often confuse orbital angular momentum with spin. I am still struggling with all the terms in QM. :-)
  11. Sep 11, 2009 #10


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    Well, spin is angular momentum, just not all of the angular momentum. :smile:
  12. Sep 11, 2009 #11
    I once played around with the electric charges of quarks and electron/positron and stumbled over this: If you consider these "elementary subparticles" to each be composed of 6 partial charges of either -1/6 og + 1/6 you end up with a description of the constituents of matter and antimatter.

    1/6,1/6,1/6,1/6,1/6,1/6 = 6/6= charge 1 = positron
    -1/6,1/6,1/6,1/6,1/6,1/6 = 4/6 = charge 2/3 = upquark
    -1/6,-1/6,1/6,1/6,1/6,1/6 = 2/6 = charge 1/3 = antidownquark
    -1/6,-1/6,-1/6,1/6,1/6,1/6 = charge 0 = neutrino
    -1/6,-1/6,-1/6,-1/6,1/6,1/6 = - 2/6 = charge -1/3 = downquark
    -1/6,-1/6,-1/6,-1/6,-1/6,1/6 = - 4/6 = charge -2/3 = antiupquark
    -1/6,-1/6,-1/6,-1/6,-1/6,-1/6, = -6/6 = charge -1 = electron

    I have no idea whether this is pure coincidence or is part of an explanation of why the subparticles have the relative charges they have. But it simplifies the picture for a non-physists as I am.

  13. Sep 11, 2009 #12

    Vanadium 50

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    It's just a restatement that charge is quantized in units of 1/3 of the electron charge.
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