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Number of photons/volume surrounding radio transmitter

  1. Feb 6, 2009 #1
    1. The problem statement, all variables and given/known data

    Seeking a method of calculating the number of photons instantaneously present within a given volume surrounding a radio transmitter at given power and frequency.

    2. Relevant equations

    [tex]E=hv[/tex], and other equations involving power and wavelength.

    3. The attempt at a solution

    I have no problem calculating the photon energy, and number of photons/second at a given frequency and transmitter power. But how to calculate the number of photons within a given spherical volume, with the transmitter in the center (assuming spherically-symmetrical pattern)?

    For example: number of photons within the near-field at x watts and y frequency (I know things can get complicated in the near-field). This is for my own curiosity and is not a textbook question (at least not one that I am aware of). I do not know where to start.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 6, 2009 #2


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    Science Advisor

    If, as you say, you have no problem with finding the number of photons of a given wavelength produced in, say, a second, then just determine how many of those photons will still be within the given radius of the source. Assume that the photons are produced at a constant rate during that second and that they move away from the source with speed, of course, c.
  4. Feb 7, 2009 #3
    Thank you HallsofIvy. I was getting confused about the near-field, but real emitted photons are the only thing we have to work with you are right.
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