Speed of light in pure Hydrogen

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Discussion Overview

The discussion centers around the speed of light in hydrogen, particularly in the context of its refractive index and how it varies with gas density and pressure. Participants explore calculations and assumptions related to the speed of light in a hydrogen environment, including the effects of density and the accuracy of measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant asks about the speed of light in hydrogen and where to find relevant data, noting that the question is vague due to the dependence on gas density.
  • Another participant suggests that the speed of light would not change significantly in a vacuum with a single hydrogen atom.
  • A participant proposes a scenario with a specific volume of hydrogen gas and inquires about the speed of light in that context.
  • There is a discussion about the refractive index of hydrogen at standard temperature and pressure (stp), which is noted to be 1.000132.
  • One participant questions whether the change in refractive index is proportional to gas density.
  • A calculation is presented by a participant claiming to have determined the speed of light in hydrogen, resulting in a value that is almost equal to the speed of light in a vacuum.
  • Another participant points out an issue with the calculated speed being greater than the speed of light in vacuum, highlighting the importance of significant figures in the calculation.

Areas of Agreement / Disagreement

Participants express varying views on the calculations and assumptions regarding the speed of light in hydrogen, with no consensus reached on the accuracy of the calculations or the implications of the refractive index.

Contextual Notes

There are unresolved issues regarding the accuracy of measurements and the dependence of the refractive index on gas density and pressure. The discussion does not clarify the constant needed for calculations involving hydrogen.

Arnaho
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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 !
 
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Arnaho said:
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 !

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.
 
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 ?
 
Arnaho said:
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 ?

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

Zz.
 
Oops ! Let's assume the density is 0.0899 kg/m3. How should I proceed now ??!
Thanks for your answers.
 
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
 
mgb_phys said:
The refractive index increases linearly with pressure (for an ideal gas) but i don't have the constant for hydrogen

Wouldn't (n-1) simply be proportional to the gas density?
 
Redbelly98 said:
Wouldn't (n-1) simply be proportional to the gas density?

Yes sorry, I meant (n-1) rather than n. We tend to assume (n-1) .
But the poster presumably still needs the constant.
 
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 !
 
  • #10
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.
 
  • #11
Okay, Thanks ! I will try with this and let see what comes up !
 

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