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Mean free path

  1. Dec 29, 2014 #1
    1. The problem statement, all variables and given/known data
    What is the mean free path of an N2 molecule in an ultra-high-vacuum chamber at a pressure of 10-10mbar?

    2. Relevant equations
    λ=1/(√2)nσ
    number density n, collision cross-section σ
    p=nkT
    pressure p, temperature T
    σ=πd2
    d molecular diameter

    3. The attempt at a solution
    λ=kT/(√2)πpd2
    where we know p and I can estimate d to be around 10-10m. However I am not given T, and I don't really see how I could know what it is...
     
  2. jcsd
  3. Dec 29, 2014 #2

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    At which point, you're free to assume a temperature. What's a good standard temperature for reference data?
     
  4. Dec 30, 2014 #3
    Standard temperature, 0degc. Thanks.
     
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