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Relation between QED photon frequency and classical EM frequency

  1. Aug 4, 2014 #1
    Hello,

    I read the Feynman's QED book, where I learned that a photon has a intrinsic property called frequency. This property affect, for example, the interference profile when we have a lot of photon together. Ok.

    Now, thinking on an conventional antenna. When we have a 100kHz signal on it, it means that the photons being emitted have a frequency of 100kHz? For me it seems that the thing is not like this, it seems to me that the frequency emitted by an antenna is more relate to the quantity of photons being emitted each time... So, what frequency are these photons?

    I may be missing a detail, or I may be completely wrong..

    Best Regards,
    Alexandre
     
  2. jcsd
  3. Aug 4, 2014 #2

    bhobba

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    Each individual photon has that frequency as can be seen in the double slit experiment when only a single photon is present.

    But care is required here. Feynmans book, as excellent as it is, is like many books at the lay or beginning level of physics. It isn't quite true - the issues being fixed up in more advanced treatments its very difficult to discuss except at an advanced technical level eg:
    https://www.physicsforums.com/showthread.php?t=763781

    This applies to the very existence of a single photon for example. In the correct theory - Quantum Field Theory - it actually consists of creation and annihilation operators - without discussing what that even means - which is itself an advanced issue.

    Thanks
    Bill
     
    Last edited: Aug 4, 2014
  4. Aug 4, 2014 #3
    No, the quantity i.e number of photons emitted is the intensity or the amplitude squared.

    Frequency = speed of light * wavelength

    For single photons the frequency is a slightly different concept:

    frequency = E / h which is Energy divided by planck's constant.
     
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