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Cosmic microwave background radiation

  1. Dec 23, 2012 #1
    1. The problem statement, all variables and given/known data

    The cosmic microwave background radiation has a blackbody type spectrum. Determine its max frequency and the correspondent wavelenght. Verify if found frequency is a microwave frequency and compare with the following curve:


    Untitled(2).jpg



    2. Relevant equations

    Using the Wien Law displacemente, and knowing that CMBR has a thermal black body spectrum at a temperature of 2.725 K. We can easily calculate the wavelength peak and its frequency.

    λmax = 1,06mm

    frequency = λmax/c = 2,83E11HZ


    We can verify that the frequency that we obtained corresponds to the microwave frequency.

    But when i am comparing with this curve Untitled(2).jpg , i did not find any relation...

    I just do not know what is the relation of the graphic with the obtained results.

    Anybody to help? Help is always appreciated.!!!
     
    Last edited: Dec 23, 2012
  2. jcsd
  3. Dec 23, 2012 #2

    mfb

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    Staff: Mentor

    That is a tricky problem.

    The curve shows the frequency-dependence of the intensity (waves/cm is proportional to frequency) - you can calculate the wavelength which corresponds to its peak, and it will not agree with your wavelength.

    This is not an error on your side, it is a surprising mathematical result: If you switch between wavelength and frequency dependence, you get different positions of the peaks, as "per wavelength" on the y-axis is different from "per frequency".
     
  4. Dec 26, 2012 #3
    So, the difference is the switching from wavelength to frequency dependence. The results are "mathematically" equal?
     
  5. Dec 26, 2012 #4

    mfb

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    Staff: Mentor

    The intensity maximum of the wavelength is different from intensity maximum of the frequency - even if the curves correspond to the same spectrum.
     
  6. Dec 26, 2012 #5
    Understood!

    Thanks a lot for the help!
     
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