Q 11-12-009NEETNEET 2020Top questionEasy
The mean free path for a gas, with molecular diameter d and number density n can be expressed as :
Answer: (B) $\dfrac{1}{\sqrt{2}\,n\pi d^2}$
Concept. A molecule sweeps a collision cylinder of cross-section $\pi d^2$; the motion of the others adds the factor $\sqrt2$.
Step 1. Mean free path.
$$\lambda = \frac{1}{\sqrt2n\pi d^2}$$
Answer. $\dfrac{1}{\sqrt2n\pi d^2}$ (Option B).
Solution by Sreeraj P, M.Sc Physics