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Homework Help: Atmospheric pressure and density.

  1. Jun 5, 2006 #1
    My question states:

    Given that the ground-level pressure of the Earth’s atmosphere is [tex]1.033 *10^5 N m^−^2,[/tex] calculate the mass of the atmosphere. If the ground-level atmospheric density is [tex]1.293 kg m^−^3[/tex], calculate the scale height.

    For the first bit, I used P=nKT, assuming a temperature of 300K, and I then calculated the number of molecules per unit area, and multiplied this number by the surface area of the Earth. I then assumed that the atmosphere was made entirely of Nitrogen and so multiplied the number of molecules by the mass of a molecule. I ended up with the answer [tex]5.99*10^1^4[/tex] kg. Does this sound about right?

    For the second part I am totally stumped. Surely if you put the height in as 0, that will tell you nothing about the scale height.
     
  2. jcsd
  3. Jun 5, 2006 #2

    Hootenanny

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    Apparently, the total mass of the atmosphere is around 5.3x1018 kilograms according to http://hypertextbook.com/facts/1999/LouiseLiu.shtml" [Broken]. You may want to factor in oxygen as a fifth is a significant proportion. Also, try taking the earths median temperature (which is about 250k)

    The scale height is defined as being The height in the atmosphere where pressure is e-1 times its value at the surface, perhaps http://scienceworld.wolfram.com/physics/PressureScaleHeight.html" [Broken] can be of some help. :smile:
     
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  4. Jun 5, 2006 #3
    They still don't give me the required order of magnitude. This is going to be a very hard exam tomorrow.
     
  5. Jun 5, 2006 #4

    Hootenanny

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    I've just noticed something;

    I hope you mean pV = nkT
     
  6. Jun 5, 2006 #5

    Hootenanny

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    Although, accoring to Wiki (I hesitate to use this a source);

     
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