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Homework Help: Absorption Spectra

  1. Sep 16, 2009 #1
    If you're reading a graph of absorption coefficient(cm^-1) versus wavelength(nm), how can you dtermine if the solution is optically dilute? What about optically thick? Thanks
  2. jcsd
  3. Sep 16, 2009 #2
    Well as the absorbtion coefficient is per cm, i am guessing the higher it is the more light is being absorbed when travelling through a cm of the substance. So the optically diluter substance is probably the one with the lower coefficient.
  4. Sep 16, 2009 #3
    I agree, unfortunately I'm not comparing two spectra, but rather just answering for a variety of spectra is the solution optically dilute? Is it Optically thick? And not sure where the cut off is, can't find a value anywhere
  5. Sep 16, 2009 #4
    K i looked on wikipedia and the equation for absorbtion coefficient is:

    I = Io e^-ax

    Where I is transmitted intensity, Io is incident intensity, a is the attenuation coefficient and x is the thickness of the substance. Rearranging for a:

    a = ln(Io/I)

    If we try some values:

    When 75% of light is transmitted a = 0.28

    When 50% of light is transmitted a = 0.69

    When 25% of light is transmitted a = 1.39

    Maybe that will help you
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