For a molecule of an ideal gas, the number density is $2 \sqrt{2} \times 10^8 \mathrm{~cm}^{-3}$ and the…

For a molecule of an ideal gas, the number density is $2 \sqrt{2} \times 10^8 \mathrm{~cm}^{-3}$ and the mean free path is $\frac{10^{-2}}{\pi} \mathrm{cm}$. The diameter of the gas molecule is
  1. $5 \times 10^{-4} \mathrm{~cm}$
  2. $0.5 \times 10^{-4} \mathrm{~cm}$
  3. $2.5 \times 10^{-4} \mathrm{~cm}$
  4. $4 \times 10^{-4} \mathrm{~cm}$

Solution

Mean free path, $ \begin{aligned} \lambda & =\frac{1}{\sqrt{2} \pi n d^2} \\ \Rightarrow \quad d^2 & =\frac{1}{\sqrt{2} \pi n \lambda}=\frac{1 \times \pi}{\sqrt{2} \times \pi \times 2 \sqrt{2} \times 10^8 \times 10^{-2}} \\ \Rightarrow \quad d^2 & =\frac{1}{4 \times 10^6} \\ \Rightarrow \quad d & =\frac{1}{2} \times 10^{-3} \mathrm{~cm} \\ \Rightarrow \quad d & =5 \times 10^{-4} \mathrm{~cm} \end{aligned} $

Asked in: AP EAMCET 2018 (22 Apr Shift 1)

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