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Snell's law

  1. May 3, 2008 #1
    For Snell's law n2sin(theta2)=n1sin(theta1), I know that air has an index of refraction of approximately 1. But how do I find the actual value for the index of refraction if I know the temperature jump and pressure? I know that from what I am given, I can find the densities of the air, but then how do I use the densities to find the index of refraction?
     
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  3. May 3, 2008 #2

    Redbelly98

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    A Google search on
    air "refractive index"
    led me here:
    http://www.strw.leidenuniv.nl/~mathar/progs/prWaterWeb.html
    Calculates (n-1) depending on temperature, pressure, humidity, and even CO2 content of the atmosphere!

    Do you happen to have a particular application or use in mind? Eg., ray tracing calculation, atmospheric distortion, solving a homework problem, other?
     
  4. May 3, 2008 #3

    olgranpappy

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    well. I think you could look up the dielectric constant ([itex]\epsilon[/itex], where [itex]n^2=\epsilon[/itex]) at different densities. but also, if you know the dielectric constant at some given number density ([itex]n_1[/itex]) then to find it at a different density you could use
    [tex]
    \frac{\epsilon(n_2)-\epsilon(n_2)}{\epsilon(n_1)-1}=\frac{n_2-n_1}{n_1}
    [/tex]

    ...and, sorry for using the symbol n for two different things... my bad, in the equation it is number density, not index of refraction
     
    Last edited: May 3, 2008
  5. May 3, 2008 #4
    this question is for a homework problem. It seems that every source I look at, the dielectric constant for air at 1 atm is 1.00059. Is this value safe to assume for all temperatures?
     
  6. May 3, 2008 #5

    Redbelly98

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    No, it will change with temperature and pressure. The denser the air, the higher the value.
     
  7. May 3, 2008 #6
    Is there an equation that relates the density to the index of refraction?
     
  8. May 3, 2008 #7

    olgranpappy

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    i gave it to you
     
  9. May 3, 2008 #8

    Redbelly98

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    You can do pretty well by assuming (n-1) is proportional to the air density.
     
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