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Speed of light in pure Hydrogen

  1. Sep 29, 2008 #1
    Hello Everyone

    Can anyone tell me what is the speed of light in hydrogen or may be where can I find that for all the elements.
    Has these datas available already in or books.
    Thanks in advance !
     
  2. jcsd
  3. Sep 29, 2008 #2

    ZapperZ

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    This is a very vague question, because it depends on the gas DENSITY. I could have only one hydrogen atom in a vacuum and the speed of light would not change by any noticeable means.

    Zz.
     
  4. Sep 29, 2008 #3
    Hi Zz. !!
    Thanks ! Yes of course ! Say we are in space with 1m3 of H2 trapped inside a chamber. And now if we pass the light thru it, than can we know the difference in the speed of light compared to its original ?
     
  5. Sep 29, 2008 #4

    ZapperZ

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    You've just given me the volume of the gas, not its density.

    Zz.
     
  6. Oct 3, 2008 #5
    Oops !!! Lets assume the density is 0.0899 kg/m3. How should I proceed now ??!!!
    Thanks for your answers.
     
  7. Oct 3, 2008 #6

    mgb_phys

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    At stp the refractive index of hydrogen (H2) is 1.000 132 (for Sodium D line probably)
    The refractive index increases linearly with pressure (for an ideal gas) but i don't have the constant for hydrogen
     
  8. Oct 3, 2008 #7

    Redbelly98

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    Wouldn't (n-1) simply be proportional to the gas density?
     
  9. Oct 6, 2008 #8

    mgb_phys

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    Yes sorry, I meant (n-1) rather than n. We tend to assume (n-1) .
    But the poster presumably still needs the constant.
     
  10. Oct 6, 2008 #9
    Hello again, So I calculated the light speed in H2 and its value is this 299960405.22 m/s. Almost equal to its speed in vacuum. This is how I did, I got the refractive index for H2 and its 1.000132. And 1/1.000132 will give us 0.99986.... when multiplied with the Speed of light in vacuum ie, 3x10^8 m/s we will get the speed of light in H2. Please correct me if am wrong. Thanks !!!!
     
  11. Oct 6, 2008 #10

    Redbelly98

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    There is a problem that your answer is actually greater than c! The issue here is with the accuracy of your answer (i.e. number of significant figures)

    If you're using 3x108 m/s for c, that's only 1 significant digit of accuracy, so the answer for H2 would still be 3x10^8 m/s.

    Even if you use 3.00x108 m/s, that still won't change significantly when divided by 1.000132.

    Better yet: use 2.997925x108 m/s. That has the same number of significant figures (7) as the refractive index.
     
  12. Oct 8, 2008 #11
    Okay, Thanks !! I will try with this and let see what comes up !!
     
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