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Asked in NEET (Oct.) 2020 · Mean free path and its dependence
Idea: the mean free path is the distance a molecule covers before its collision cross-section sweeps out one other molecule.
Mean free path: l=1/(√2 π n d²), with n the number density.
Only d varies in this question, so the number density is held fixed.
The diameter appears only in the cross-section π d², in the denominator.
l∝1/(d²).
The √2 comes from the other molecules moving too; it changes the constant, not the power of d.
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