1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Intensity and frequency of radio waves

  1. Apr 13, 2013 #1
    Hi, I am not a physicists and have been trying to understand some basic concepts about electromagnetic waves in the context of telecommunications.

    Now, this is what I know so far: the energy of electromagnetic waves is proportional to it's frequency (E = h*f), and basically it's the energy carried by a single photon.

    The intensity of an electromagnetic wave is the amount of power transferred per unit area, and can be described as the amount of photons * energy per photon.

    IF these assumptions are correct, then the intensity could be increase in two ways: by increasing the frequency (energy per photon) or by increasing the voltage used to generate the wave (number of photons). Either of these two would yield more energy transferred and therefore higher intensity.

    Is this reasoning correct?
  2. jcsd
  3. Apr 13, 2013 #2


    User Avatar

    Staff: Mentor

    I would say rather, that the energy of a single quantum (photon) of an electromagnetic wave is proportional to its frequency via E = hf.

    Usually, an electromagnetic wave "contains" many many many [...] many many photons, so its (total) energy is some very very very [...] very very large multiple of hf.
  4. Apr 13, 2013 #3
    So is it logical to think that by increasing the frequency, the intensity at a distance A meters would be greater than with lower frequency?
  5. Apr 13, 2013 #4


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Yes - if you made sure that your transmitter was radiating the same number of Photons per second. That is an unlikely scenario because transmitters tend to operate on the basis of Volts and Amps - i.e. Watts - in which case, for a given radiated power, the number of Photons would be inversely proportional to the frequency of the transmission.
  6. Apr 13, 2013 #5
    It is not difficult to calculate the number of photons emitted per second required to emit a particular power.
    If a light bulb emits 100W (100J/s) of yellow light then by using E = hf (with f = FREQUENCY of yellow light) you can calculate the number of yellow photons emitted per second.
    If it is 100W of gamma radiation you will get a vastly different answer.. You can usually detect individual photons of gamma radiation (clicks on a geiger counter) but you cannot easily detect individual yellow photons.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook