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Homework Help: FM/AM stations and photons. please help!

  1. Apr 8, 2010 #1
    1. Two radio stations have the same power output from their antennas. one broadcasts on FM band at 105.2 MHz and other on the AM band at 701kHz. Which one emits more photons per second? Or do they emit the same amount of photons per second? Explain answer

    2. I don't know if i've been doing it right. I've been using einstein's photoelectric effect to get the energy of each (E=hf), but I don't know how to relate this to the actual emition of photons. Please help! I'm the biggest novice :(

    3. (105.2 x 10^6 s^-1) x (6.626 x 10^-34) = 6.97 x 10^-26

    (701 x 10^3 s^-1) x (6.626 x 10^-34) = 4.64 x 10^-28
  2. jcsd
  3. Apr 8, 2010 #2
    You've found the energy of the FM station's photons, and the energy of the AM station's photons.

    If you know that they both have the same power output, that means that each station is pumping out enough photons of energy [tex]E=hf[/tex] every second, so that the energy per unit time, equals the output, [tex]P[/tex]. How would you relate that mathematically? Try using an arbitrary symbol like [tex]n[/tex] for the number of photons emitted per second.
  4. Apr 8, 2010 #3
    hmmm... would it be

    N photons/sec = Power / photon energy

    i'm new to making equations so i don't really know how to write it out, but it is making some sense in my head and it's working. thanks alot! I justdon't know how to put it into an acceptable equation form, aka what the value of P should be.
  5. Apr 8, 2010 #4


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    Just think about it. E=hf gives the energy EACH photon has. Which radio station gives off lower-energy photons? Since the photons have lower energy, does the station have to give off more or less photons to emit with the same power as the other station?
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