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Photons & their relation to charge

  1. Oct 28, 2011 #1
    Hello All,

    Im having a doubt. Generally, the electromagnetic radiation/photons are created when electrons accelerate in a field or fall from their excited state to normal state etc. Photons are waves of electrical & magnetic fields. Since, photons originate from electrons, shouldnt they have negative charge flavor ?
    cause, when a proton (positive particle) accelerate in a field, they also emit photons. These photons cant be the same as those generated by electrons right ?
    does maxwells equations permit to have these 2 flavors (+ve & -ve) for electromagnetic radiation ?
     
  2. jcsd
  3. Oct 28, 2011 #2

    Dale

    Staff: Mentor

    Charge is conserved, so if a photon had a negative charge then that would leave the electron chargeless.
     
  4. Oct 28, 2011 #3
    thanks...but when you say photons are oscillating electromagnetic fields...are these fields negative or positive in nature ? if charge is conserved and is with electrons...then, there should not be any electric or magnetic aspect for a photon ?
     
  5. Oct 28, 2011 #4
    I think you are confused - photon charge flavors? Light is an oscillating electromagnetic wave - it has no charge or mass, and the oscillating fields vary rapidly in time and space from positive to negative and back again (fields being vectors with directions).
     
  6. Oct 28, 2011 #5
    actually, i was just accepting this without thinking much. But when you say, photos are oscillating fields from positive to negative and back again, where did this positive oscillation come from ? electrons can give rise only to negative fields if im thinking correct..
     
  7. Oct 28, 2011 #6
    Electrons? What does an electron have to do with an electromagnetic wave? It's a wave, with peaks and dips that are positive and negative relative to the average. An isolated electron carries a negative charge and therefore has an electrostatic field that is directed towards it. A photon has no charge and has an average field equal to zero.
     
  8. Oct 28, 2011 #7
    ravisastry, you seem to be confusing "electric charge" with "electromagnetic wave polarization". They are different things. The direction that a wave oscillates (up-and-down, side-to-side, round in circles) is called the wave's polarization. The wave polarization is a classical concept and it's quantum counterpart is the photon's spin, not it's charge. Photon's have spin but not charge.
     
  9. Oct 28, 2011 #8

    jtbell

    User Avatar

    Staff: Mentor

    Start with a stationary electron. At any point, the electric field produced by the electron points towards the electron (radially inward) and is "stationary." (doesn't change in magnitude or direction).

    Now shake the electron so it oscillates back and forth along a line. This causes the electric field at every point to oscillate also. You now also have an oscillating magnetic field because the oscillating electron behaves like an oscillating electric current. The oscillating electric and magnetic fields together form an electromagnetic wave that spreads outward from the oscillating electron. This is basically an oscillating dipole. See here for an animation of the magnetic field that it produces:

    http://en.wikipedia.org/wiki/Dipole#Dipole_radiation

    If you Google for "electromagnetic dipole radiation" you should be able to find similar pictures for the electric field.
     
  10. Oct 29, 2011 #9
    no, Im not confusing charge with wave, rather looking for similarities with electric field and field within photon. as mentioned in the next reply, oscillation of electron produces oscillating field, but it can only be negative field, where as in photon, you have positive field as well, which confuses me.
     
  11. Oct 29, 2011 #10
    is it possible tat the crest and trough of photon, has negative field, but in opposite direction ? this will also cancel the net charge, as the fields are in opposite direction
     
  12. Oct 29, 2011 #11
    I think you just aren't listening here. There is no charge, this has been pointed out several times - a photon does not have a charge. Positive and negative refer to directions, only - that's the only meaning of positive and negative. A positive charge moves by definition in the direction of a positive field.
     
  13. Oct 29, 2011 #12
    What leads you to this conclusion? There is no such theory that suggests this is accurate.

    For example, a photon is massless and chargless...any particle with mass or charge cannot be a photon any more than an electron can have positive charge or no mass.....

    Besides, a static magnetic field (say from a magnet) does not originate from either accelerating or decelerating electrons......and an electromagnetic field around a current carrying conductor is based on the steady velocity of electrons, not acceleration, so now you'll have to postulate several different kinds of EM fields.
     
  14. Nov 11, 2011 #13
    sorry, was thinking on this and somehow...not convinced yet. My questions are..

    2 photons(gamma rays) can combine (under special circumstances) to form an electron and a positron. pls check http://en.wikipedia.org/wiki/Two-photon_physics

    from where did these charges of electrons and positrons originate ? the 2 initial photons didnt had any charge right ? this assumption of photons not carrying any charge isnt convincing in this case.

    The photons should be having a latent charge.... :-|
     
  15. Nov 11, 2011 #14
    There is no "latent charge" in the initial photons, in established physics. The mathematical model that describes these phenomena (QED) is extremely successful and accurate. You are of course free to speculate and try to form an improved theory that fits better with your notions of how microscopic phenoma ought to work. If you come up with a concrete theory concerning this latent charge, I'm sure there are folks here that would be interested in discussing its merits with you.

    In short, the +1 and -1 charges of the created electron-positron pair appears absolutely out of nowhere, according to QED. Actually, the charges are inherent properties of these particles.
     
  16. Nov 11, 2011 #15

    Drakkith

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    Staff: Mentor

    Two uncharged photons can produce 2 charged particles because the + and - of the electron and positron equal 0 net charge. This means that charge is conserved. The start and end products both have 0 net charge combined. Two photons could NOT produce 2 electrons and a positron, or just 2 electrons, because then you would have extra negative charge left over.

    Also, if you have an oscillating electric field, then 50% of the time it is + and 50% of the time it is -. So over any period of time involving at least 1 oscillation the net charge equals out to 0. (Not saying that's actually how it works, but trying to help you visualize it) The reality is that you probably won't ever understand it unless you actually study QM and QED and see the math and how it all works. You are trying to understand a puzzle by looking only at a few pieces, it just isn't going to work.
     
  17. Nov 11, 2011 #16
    this is not convincing :(...its like creating things out of nothing....ppl always talk about end products and say there is + and -, hence net charge is zero. My question is...where/how did + and - did come in the first place ?
    my hypothesis...charge has to be conserved as well, not just the total charge.
    A negative/positive charge can neither be created nor destroyed...but can only be transformed :)
     
  18. Nov 11, 2011 #17

    Drakkith

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    Staff: Mentor

    I think you just said the same thing that has been said already only in different words.
    As for WHERE the charges come from, I don't know if it's possible to know exactly. We don't know where any intrinsic properties of particles come from, we only know how they behave.
     
  19. Nov 11, 2011 #18

    Dale

    Staff: Mentor

    The total charge is 0+0=0 before the interaction and the total charge is +1-1=0 after. Charge is conserved. There is no need to postulate some nonzero charge of the photon.
     
  20. Nov 11, 2011 #19
    One of the important lessons learned from the discovery of quantum mechanics is that one should be careful to apply ones preconceived notions about how things "should" work according to everyday experience, when discussing microscopic phenomena.

    That said, if you have the necessary background in physics, perhaps you'll probably enjoy the old "Dirac sea" interpretation of particles/anti-particles:

    http://en.wikipedia.org/wiki/Dirac_sea" [Broken]
     
    Last edited by a moderator: May 5, 2017
  21. Nov 11, 2011 #20

    Dale

    Staff: Mentor

    Then how can an electron in an atom absorb a photon? Remember, your hypothesis must be compatible with all interactions, not only two-photon interactions.
     
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