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Frequency of a photon?

  1. May 19, 2005 #1
    Could someone please explain to me what is meant by the frequency of a photon? Aren't photons basically particles? Isn't frequency an attribute that we would generally associate with waves rather than particles? So what is it that we are actually measuring when we talk about the frequency of a photon?
    Thanks guys
  2. jcsd
  3. May 19, 2005 #2
    Good question. I would like also to know what is, really, the quantum momentum of a particle.

  4. May 19, 2005 #3


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    Well,if you had read about blackbox radiation and Planck's 1900 analysis,you'd have gotten the right idea.

  5. May 19, 2005 #4
    We're measuring the photon's energy which is related to the frequency of the wave by E = hf, where h = Planck's constant.
  6. May 19, 2005 #5
    Light was previously considered to be a wave, since it bends arround corners and give interferrence patterns etc. Then people meassured black body radiation and planck discovered that things work better if energy comes in packets, aslo einstein used this energy in packets idea to explain the photo electric effect. Nowadays things are considered to obey the laws of quantum mechanics and thus all has frequency and so on..
  7. May 19, 2005 #6
    Hi madness,
    Only the length of a photon has been known since the rainbow was analyzed a couple of centuries ago. Then when the velocity of light was discovered a century ago someone divided the distance traveled by a photon in one second by the length of the photon and called it "frequency" rather than the number of unitary photons per second. Go figure. Jim
  8. May 19, 2005 #7


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    Say what ?What length of the photon...?The photon is a masless pointlike particle.

    The velocity of light was not discovered,but measured by Bradley,Ro/mer,Fizeau etc.

    Last edited: May 19, 2005
  9. May 19, 2005 #8
    Is it the policy of this forum to allow people to continually write nonsense in a confident fashion? (Not referring to you, of course, Daniel).
    Last edited: May 19, 2005
  10. May 19, 2005 #9


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    Hi juvenal,

    When someone signs up to becoming a PF member, the agree to abide by certain guidelines (freely available on the PF website).

    Writing nonsense is not against the guidelines, nor is confidence in how one writes a post - we do not wish, in any way, to restrict free enquiry ... initially. If a PF member wishes/chooses to remain ignorant, and continue to ask questions that have been answered before (even if they're from the same member!), so be it.

    OTOH, if they continue to confidently post nonsense (not questions), we hope that other PF members will report such behaviour; one or more moderators will then review the relevant posts, and take whatever actions may be appropriate.

    I hope this clarifies things for you.

    Kind Regards
  11. May 19, 2005 #10
    Hi Daniel and juvy (and I don't mean you Daniel),
    The length of a QM Sodium D yellow photon is 5,890 Angstroms(10^-10 meters) and there are literally many many different spectral photons and not one is a point particle. Oh yes' forgive me! - photons were never discovered they were just measured without having been discovered. Cheers, Jim
  12. May 19, 2005 #11


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    That's the WAVELENGTH of the radiation emitted by sodium.

    Photons are points particles.

  13. May 19, 2005 #12
    Let me waste some of my time then:

    You might be talking about wavelength and not length. These are two different things. The wavelength of a moving bowling ball, for example, according to quantum mechanics, is not the same as the the length of a bowling ball.

    Even so, the distance travelled by a photon in one second is approx 3E+08m. You divide by the wavelength of the photon, and you get a unitless number. Frequency is in units of Hz which have units of inverse seconds.
  14. May 19, 2005 #13

    Claude Bile

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    The number of times the electromagnetic field oscillates per second. This determines the diffractive properties of light, as well as how the light will behave when travelling through certain media.

    Nope, particles (e.g. electrons) also posess a frequency and wavelength (Look up electron diffraction).

  15. May 19, 2005 #14


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    From post # 13 (lucky number,i guess) "Isn't frequency an attribute that we would generally associate with waves rather than particles" (by madness)
    "Nope, particles (e.g. electrons) also posess a frequency and wavelength (Look up electron diffraction)." (by Claude Bile)

    Funny,electron diffraction is properly explained in terms of de Broglie pilot waves (or if u prefer Schrödinger scalar waves),where the "k","\lambda" have the same significance as for an em wave in Maxwell's theory. :rolleyes:

  16. Jul 6, 2009 #15
    De Broglie postulated matter waves, according to him, all particles must behave as waves and vice versa, an idea resulting from Einstein's concept of a light photon.
    The wavelength is given by
    Macroscopic particles have too large momentum as compared to planck's constant(6.6*10^-36).
  17. Jul 6, 2009 #16
    The photon frequency is the wave frequency, no problem with it. A single photon is a sufficiently long wave packet (of thousands or dozens thousands of vibrations in it). So we safely speak of its frequency. Now everything, everything is waves with the following time dependence: exp(-iEt/ћ). While interaction, the initial and final states of interacting "particles" are written in QM as a product of wave functions, in particular:exp(-iE1t/ћ)*exp(-iE2t/ћ)=exp(-i(E1+E2)t/ћ). You see, the energies are added as if the waves were possessing particle energies E1 and E2. Photon is not exclusion. Photon energy and photon frequency is nearly the same thing (they are proportional to each other). That is how the wave-particle duality works in QM. Again, everytbing is a wave.
    Last edited: Jul 6, 2009
  18. Jul 6, 2009 #17


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    this is a 4 year old thread....
  19. Jul 6, 2009 #18
    Yes, indeed...
  20. Apr 1, 2011 #19
    @ juvenal; I don't mean to troll this thread on too long with questions, but I had a bit of a misconception also and I thought the bowling ball analogy was a pretty good one. So just to be clear with what I have read so far- considering a single photon to be the bowling ball- is the frequency of the bowling ball implying the movement of the bowling ball sort of shaking or "vibrating in place" even as it is headed toward the end of the lane? (like a wobbling bullet headed towards it's target) I guess a better example would be throwing a phone on constant vibrate down a hallway. Is that what the frequency of a photon is describing?
  21. Apr 1, 2011 #20
    oh god, it is old. well, if anyone can answer my previous question, many thanks
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