Related Formula
λ = kB T√(2) π σ² P$$\lambda = \frac{k_B T}{\sqrt{2} \pi \sigma^2 P}$$
where,
λ$\lambda$ = mean free path
kB$k_B$ = Boltzmann constant
T$T$ = absolute temperature in Kelvin
σ$\sigma$ = diameter of the molecule
P$P$ = pressure of the gas
Step 1: Extract and Convert Given Data
d = σ = 5 × 10⁻¹⁰ m$d = \sigma = 5 \times 10^{-10} \text{ m}$
T = 41^ = 273 + 41 = 314 K$T = 41^\circ\text{C} = 273 + 41 = 314 \text{ K}$
P = 1.38 × 10⁵ Pa$P = 1.38 \times 10^5 \text{ Pa}$
kB = 1.38 × 10⁻²³ J/K$k_B = 1.38 \times 10^{-23} \text{ J/K}$
Step 2: Substitution and Calculation
λ = 1.38 × 10⁻²³ × 314√(2) × π × (5 × 10⁻¹⁰)² × 1.38 × 10⁵$$\lambda = \frac{1.38 \times 10^{-23} \times 314}{\sqrt{2} \times \pi \times (5 \times 10^{-10})^2 \times 1.38 \times 10^5}$$
Cancel out 1.38$1.38$ from numerator and denominator:
λ = 10⁻²³ × 314√(2) × 3.14 × 25 × 10⁻²⁰ × 10⁵$$\lambda = \frac{10^{-23} \times 314}{\sqrt{2} \times 3.14 \times 25 \times 10^{-20} \times 10^5}$$
λ = 314 × 10⁻²³√(2) × 3.14 × 25 × 10⁻¹⁵$$\lambda = \frac{314 \times 10^{-23}}{\sqrt{2} \times 3.14 \times 25 \times 10^{-15}}$$
λ = 100 × 10⁻²³√(2) × 25 × 10⁻¹⁵$$\lambda = \frac{100 \times 10^{-23}}{\sqrt{2} \times 25 \times 10^{-15}}$$
λ = 4 × 10⁻⁸√(2) = 2√(2) × 10⁻⁸ m$$\lambda = \frac{4 \times 10^{-8}}{\sqrt{2}} = 2\sqrt{2} \times 10^{-8} \text{ m}$$
Pattern Recognition
The temperature 314 K$314 \text{ K}$ and π ≈ 3.14$\pi \approx 3.14$ are intentionally matched to cancel out and give a factor of 100. 1.38$1.38$ cancels completely. The rest is simply handling powers of 10.
Chapter Mix
Class 11 Physics: Kinetic Theory