Photons & their relation to charge

  • Thread starter ravisastry
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  • #1
ravisastry
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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 ?
 

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  • #2
Dale
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Since, photons originate from electrons, shouldnt they have negative charge flavor ?
Charge is conserved, so if a photon had a negative charge then that would leave the electron chargeless.
 
  • #3
ravisastry
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Charge is conserved, so if a photon had a negative charge then that would leave the electron chargeless.

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 ?
 
  • #4
JeffKoch
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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).
 
  • #5
ravisastry
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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).

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..
 
  • #6
JeffKoch
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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..

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.
 
  • #7
chrisbaird
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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.
 
  • #8
jtbell
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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.
 
  • #9
ravisastry
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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 conc and it's quantum counterpart is the photon's spin, not it's charge. Photon's have spin but not charge.

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.
 
  • #10
ravisastry
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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
 
  • #11
JeffKoch
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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

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.
 
  • #12
Naty1
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Since, photons originate from electrons, shouldnt they have negative charge..... ?

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.
 
  • #13
ravisastry
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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.... :-|
 
  • #14
torquil
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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.... :-|

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.
 
  • #15
Drakkith
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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.... :-|

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.
 
  • #16
ravisastry
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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.

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 :)
 
  • #17
Drakkith
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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 :)

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.
 
  • #18
Dale
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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 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.
 
  • #19
torquil
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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 :)

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]
 
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  • #20
Dale
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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 :)
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.
 
  • #21
ravisastry
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Then how can an electron in an atom absorb a photon?

well, it may sound weird...but my thinking says, photons(or electromagnetic radiation) are of two (or more )types/charge flavours...let me drop this before others start calling me a crack pot :P
 
  • #22
Drakkith
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well, it may sound weird...but my thinking says, photons(or electromagnetic radiation) are of two (or more )types/charge flavours...let me drop this before others start calling me a crack pot :P

Crackpot? No. Ignorant of the details of Quantum Mechanics? Yes. Just pick up a book or two and read up and you'll be fine.
 
  • #23
Dale
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well, it may sound weird...but my thinking says, photons(or electromagnetic radiation) are of two (or more )types/charge flavours...let me drop this before others start calling me a crack pot :P
Then the electron would have to emit both in order to conserve charge, and yet it is observed to emit only one. I would also recommend that you drop the idea, it is not compatible with observation.

Another problem with the idea is that this would allow an EM field to exert a non-zero force on photons. A non-zero force being exerted on a massless particle would cause all sorts of problems.

Another problem is that since photons are bosons and you can have as many bosons as you like occupying the same state. This means that regardless of how small the charge of an individual photon was you would quickly get fields with infinite charge, particularly at lower energies. This would be very noticeable, and probably incompatible with the formation of stars or life.
 
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  • #24
ravisastry
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Then the electron would have to emit both in order to conserve charge, and yet it is observed to emit only one. I would also recommend that you drop the idea, it is not compatible with observation.

Another problem with the idea is that this would allow an EM field to exert a non-zero force on photons. A non-zero force being exerted on a massless particle would cause all sorts of problems.

Another problem is that since photons are bosons and you can have as many bosons as you like occupying the same state. This means that regardless of how small the charge of an individual photon was you would quickly get fields with infinite charge, particularly at lower energies. This would be very noticeable, and probably incompatible with the formation of stars or life.

Thanks for your reply...what my line of thinking is...

Electron has charge...and so is surounded by electric field, namely negative electric field.
Similarly, proton is surrounded by positive electric fields.

These are 2 different fields...yet they exist right ?
why cant we have photons having these 2 different fields ? this should be possible...but i dont know quantum physics :(
 
  • #25
Dale
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Electron has charge...and so is surounded by electric field, namely negative electric field.
Similarly, proton is surrounded by positive electric fields.
This is not correct. The electric field does NOT come in positive and negative flavors. It simply has a magnitude and a direction, not a charge.

These are 2 different fields.
No, see above. They are the same field, just pointing in a different direction.

why cant we have photons having these 2 different fields ? this should be possible...but i dont know quantum physics :(
There are not two different fields. The photon does not have nor does it need any charge.
 
  • #26
Philip Wood
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+1 + (-1) = 0 + 0.Therefore 0 must contain both positiveness and negativeness. This reminds me slightly of what you're claiming about photons and charges. I think the meta-mathematical claim is pretty much meaningless. Apart from anything else, the word 'contains' needs defining.

Or consider this invalid claim: neutrons decay into protons, electrons and antineutrinos. Therefore those particles must live inside neutrons.
 
  • #27
ravisastry
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Dale..thanks for clarification.
Philip, i like the analogy...but
neutrons have 1 up quark, 2 down quarks
Protons have 2 up quarks, 1 down quark
and neutrinos are elementary particles, just like quarks...

so the neutrons splitting is quite possible..my next question would be... during ordinary regular interaction between light and matter....why does light interact only with electrons of materials ? why not photons getting absorbed/emitted by protons ?
 
  • #28
Drakkith
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so the neutrons splitting is quite possible..my next question would be... during ordinary regular interaction between light and matter....why does light interact only with electrons of materials ? why not photons getting absorbed/emitted by protons ?

I believe they can interact with protons. I THINK a free proton can absorb a photon and acquire something like kinetic energy. It doesn't absorb it and move to a higher energy state unless the photon is in the gamma ray energy range, as the excited states for the quarks in a proton or neutron are in the MeV range I think, instead of the eV range with electrons.
 
  • #29
Dale
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during ordinary regular interaction between light and matter....why does light interact only with electrons of materials ? why not photons getting absorbed/emitted by protons ?
That just depends on the energy of the photon. Nuclear magnetic resonance is a common interaction with protons which is used in MRI.
 
  • #30
cbetanco
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ravisastry,

Have you solved Maxwell's equations when you set the charge density to zero? You automatically get plane wave solutions to the electric and magnetic fields that travel at the speed of light. That is, by just solving the equations free of charge, you get your photons (of course, in the classical sense).

I would recommend just solving Maxwell's equations with rho=0, and see what you get.
 

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