Calculating Mean Free Path of N2 Molecule in UHV Chamber

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SUMMARY

The mean free path (λ) of an N2 molecule in an ultra-high-vacuum (UHV) chamber at a pressure of 10-10 mbar can be calculated using the formula λ=1/(√2)nσ, where n is the number density and σ is the collision cross-section. The collision cross-section for N2 can be approximated as σ=πd2, with d being the molecular diameter, estimated to be around 10-10 m. To calculate λ, the temperature (T) must be assumed, with standard reference temperature set at 0°C. This calculation is essential for understanding molecular behavior in vacuum environments.

PREREQUISITES
  • Understanding of mean free path calculations
  • Familiarity with gas laws and equations of state
  • Knowledge of molecular diameter and collision cross-section concepts
  • Basic thermodynamics, particularly relating to temperature and pressure
NEXT STEPS
  • Research the impact of temperature on mean free path calculations
  • Explore the properties of N2 molecules and their behavior in vacuum conditions
  • Learn about ultra-high vacuum (UHV) systems and their applications
  • Study the derivation and applications of the ideal gas law in various conditions
USEFUL FOR

Students in physics or engineering, researchers working with vacuum systems, and professionals involved in molecular dynamics simulations will benefit from this discussion.

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...
 
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albega said:
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?
 
Standard temperature, 0degc. Thanks.
 

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