alleryIf the mean free path of N₂ at 1 atm is ~80 nm, what is it at 0.01 atm (same T)?
A~ 8 nm
B~ 80 nm
C~ 800 nm
D~ 8 μm (mean free path ∝ 1/P)
Answer & Solution
Correct answer: D. ~ 8 μm (mean free path ∝ 1/P)
λ ∝ T/P. Reducing P by 100× increases λ by 100×: 80 nm × 100 = 8000 nm = 8 μm.
(Why vacuum coating works at low pressure — gas molecules don't collide before reaching the substrate.)
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