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The Frequency of a Photon
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by kudoushinichi
on 2007-09-28 08:28:23
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According to classical wave theory, the frequency of an electromagnetic wave is the number of complete oscillations made per second... My question is, according to the quantum theory of light, what does it mean when we say 'the frequency of a photon'? The measure of energy of a photon? (Since E=hf) What happened to frequency as in the frequency of oscillations? Since in the quantum theory, the photons aren't really oscillating (or at least, I had that impression...) Two protons are identical with each other (ie. if you are given two protons, you cannot distinguish between them since both of them looks the same). Is it the same for photons?
Shinjitsu wa itsumo hitotsu!
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Re: The Frequency of a Photon
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by
on 2007-09-28 11:25:28 (edited 2007-09-28 11:33:01)
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Feynman, who understood light and matter better than anyone else in his time, might say that the "frequency of a photon" is another way of describing the "energy of a photon". Different units, same property. A photon can be described many ways, but insomuch as those different explanations do a good job modeling nature, they are all correct. A photon is a packet of (electromagnetic) energy. A photon is a wave (in the electromagnetic field). Both can be viewed as quite accurate. Given this multiple choice question: Which statement is the most true about a photon: A) It has properties of a particle. B) It has properties of a wave. C) Both A and B are correct. D) None of the above. The "correct" answer is C. Answering A would fail to model part of the photon's behavior. Answering B would do the same. That's just about as good as we can do, in English. I'm sure you know very well the relationship between frequency and wavelength. Frequency is a measure of the number of wave crests per unit time. Wavelength is a measure of the unit length of each wave. If you know the speed of a wave, you can freely go between frequency and wavelength! No problem for a photon, since c is the known speed of all photons (in a vacuum), right? Well, with a photon, you can freely go between frequency, wavelength, AND energy! This is because, all photons of a given energy level have the same wavelength, always! They don't have any other properties to make them different. One photon of wavelength X is the same (indistinguishable) from another photon of the same wavelength! As for the question "do photons really oscillate?", I have to ask, what do you mean by "oscillate"? If you mean, moving up and down or side to side or around and around, in some CLASSICAL sense, then, no, they do not. They do, however, have a frequency, because they do have properties of a wave. The "position" of a photon, in 4-D space is a strait line. They are observed to follow a strait path unless you muck with them by, say, putting them in an electromagnetic field, or, putting an obstacle in their way, such as a mirror. Remember, photons are not waves in any "medium", so you can't measure the wave crest of the medium at any point along the wave. The only way to detect a photon in experiment is for it to excite an electron. This happens in an all-or-nothing sort of way, statistically modeled by Schrodinger's equation. 
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Re: The Frequency of a Photon
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by kudoushinichi
on 2007-09-28 16:24:14
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I think I understand it a little now... Thanks Hmm... having frequency but doesn't oscillate. Sounds confusing. But then again, matter particles such as electrons also have wave-like properties... and from what I read in The Elegant Universe, their behaviour is most intriguing...
Shinjitsu wa itsumo hitotsu!
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Re: The Frequency of a Photon
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| This also is where string theory comes in, as a single one dimentional string is thought to be isolating ie has a certain frequency value. |