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Homework Help: Atmosphere model approximation limits

  1. Nov 11, 2012 #1
    I am modelling the atmosphere as a perfect, static gas subject to uniform gravity, assuming ideal gas equation, the density is found to follow: p=A*exp(-z/H) where A is a const, z is the heigh, and L is the scale height.

    I want to know when this approximation breaks down! at what density? i am thinking that as the density goes down the approximation for he idea gas law breaks, but not quite sure if there is a specific value at which it breaks! maybe a certain number of molecules??

    thanks a million!
    Last edited: Nov 11, 2012
  2. jcsd
  3. Nov 11, 2012 #2
    Are you asking (a) What are the limitations of the ideal gas law? or (b) What are the limitations of the atmospheric density equation?

    I will address the second question. The equation you gave assumes that the temperature of the atmosphere is independent of altitude, such that the scale height is a constant. If you take into account the fact that the temperature varies, then the exponential term contains an integral, and the parameter A is temperature dependent.
  4. Nov 11, 2012 #3
    Thank Chestermiller!

    The thing is that the questions asks at which density the approximation breaks and consequently at what height, i was thinking maybe that would happen at the stratosphere, as the temperature starts to increase in their due to the absorption of UV, so above 9km!
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