Mean free path

  • Thread starter albega
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Homework Statement


What is the mean free path of an N2 molecule in an ultra-high-vacuum chamber at a pressure of 10-10mbar?

Homework Equations


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

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...
 

Answers and Replies

  • #2
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However I am not given T, and I don't really see how I could know what it is.
At which point, you're free to assume a temperature. What's a good standard temperature for reference data?
 
  • #3
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Standard temperature, 0degc. Thanks.
 

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