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B Thermal coefficient of expansion in gases

  1. Dec 1, 2016 #1
    I know that the variation in a gas' volume is equal to ΔV = γ⋅V[initial]⋅ΔΘ with ΔΘ the variation in temperature and γ=1/237 the thermal coefficient of expansion in gases. Could someone please explain to me why γ=1/237 please ?
    Thanks a lot,
  2. jcsd
  3. Dec 1, 2016 #2


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    Staff: Mentor

    Never seen this before. Do you have a source?
  4. Dec 1, 2016 #3
    From the ideal gas law, what is the derivative of volume with respect to temperature at constant pressure? (Are you sure about that 237, or should it be 273?)
  5. Dec 2, 2016 #4
    Yes, sorry, I meant 273. My phycs teacher told me this, but I hadn't quite understood. Thanks a lot.
  6. Dec 2, 2016 #5
    What about my other question?
  7. Dec 2, 2016 #6
    I haven't learned about derivatives yet.
  8. Dec 2, 2016 #7
    Are you familiar with the ideal gas law?
  9. Dec 2, 2016 #8
    I think - a perfect gas is a gas in which there are no chemical reactions between the molecules. I'm not sure, I'm just starting to learn about gases and expansion etc.
  10. Dec 2, 2016 #9
    For your background it may be more useful to read about the experimental side of the thermal expansion. The 273 value can be determined by extrapolating experiments on gases, as described in section 17.4 of the link below:


    If you plot the volume versus temperature at constant pressure, you get a straight line which will correspond to zero volume for a temperature of about -273 Celsisus.
    The nice thing is that this extrapolated temperature is about the same for all gases (exactly the same for ideal gases, of course). So this led to the definition of an "absolute" temperature scale.
  11. Dec 2, 2016 #10
    Google "Ideal Gas Law"
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