Mean Free Path (λ = 1/(√2 π d² n) with n number density N/V)

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λ = 1/(√2 π d² n) with n number density N/V

What each symbol means

SymbolWhat it stands for
dMolecular diameter (effective collision diameter)
nNumber of molecules per unit volume (m⁻³)
λMean free path (m)

When to use this

Hard-sphere kinetic model; ideal gas number density; stationary target correction gives √2 in denominator (relative motion).