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Homework Help: Joules - Quanta

  1. Apr 24, 2005 #1
    Hey I am in need of some assistance. In a problem I need to transfer Joules to quanta but am unsure on how to do it. A radio station is going at 200 KW with a frequency of 103.7 MhZ. So 200,000 Joules a second need to be converted to quanta. Thanks in advance!
     
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  3. Apr 24, 2005 #2

    Andrew Mason

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    You want to find the number of photons (radio frequency ones) emitted per second.

    Start with [tex]E_{photon} = h\nu[/tex]

    The total energy in one second is equal to the sum of the energies of all the photons emitted in one second. I think you can work the rest out.

    AM
     
  4. Apr 24, 2005 #3
    Is the E=hv the sum of the energy for all the photons?
     
  5. Apr 24, 2005 #4
    No. This equation will give you the energy that is released in one photon.

    The Bob (2004 ©)
     
  6. Apr 24, 2005 #5
    Ah and then the total energy has to be equal to the 200 KW..but what is the speed on the photon? C?
     
  7. Apr 24, 2005 #6
    You do not need the speed. You need Planck's Constant.

    The Bob (2004 ©)
     
  8. Apr 24, 2005 #7
    E=HV, yeah nevermind, meant F..thanks this one makes sense now
     
  9. Apr 24, 2005 #8

    Andrew Mason

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    So how many photons are produced in one second?

    AM
     
  10. Apr 24, 2005 #9
    Personally I get a rather large number (which is too be expected) but should it be this (2.9 x 1030 photons) big???

    The Bob (2004 ©)
     
  11. Apr 24, 2005 #10
    I got a huge number as well..It is large but I expected it to be of such size
     
  12. Apr 24, 2005 #11
    Was it the same as my number???

    The Bob (2004 ©)
     
  13. Apr 24, 2005 #12
    You didnt give a number :)
     
  14. Apr 25, 2005 #13
    It was in white.

    The Bob (2004 ©)
     
  15. Apr 26, 2005 #14

    Andrew Mason

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    It is that big. At 1000 km, the intensity would be about 2 x 10^17 photons/m^2 per second. And that is just a measly radio antenna. You can see why a quasar can still provide detectable radio signals on earth despite being billions of light years away.

    AM
     
  16. Apr 26, 2005 #15
    You can. So much for telescopes that can detect a few photons of light, use radar discs. :smile:

    The Bob (2004 ©)
     
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