The mean free path of a molecule of diameter 5 × 10⁻¹⁰ m at the temperature 41°C and pressure 1.38 × 10⁵ Pa, is given as ____ m. ( Given~kB = 1.38× 10⁻²³ J / K).

Solution & Explanation

Related Formula
λ = kB T√(2) π σ² P

where, λ = mean free path kB = Boltzmann constant T = absolute temperature in Kelvin σ = diameter of the molecule P = pressure of the gas

Step 1: Extract and Convert Given Data

d = σ = 5 × 10⁻¹⁰ m T = 41^ = 273 + 41 = 314 K P = 1.38 × 10⁵ Pa kB = 1.38 × 10⁻²³ J/K

Step 2: Substitution and Calculation
λ = 1.38 × 10⁻²³ × 314√(2) × π × (5 × 10⁻¹⁰)² × 1.38 × 10⁵

Cancel out 1.38 from numerator and denominator:

λ = 10⁻²³ × 314√(2) × 3.14 × 25 × 10⁻²⁰ × 10⁵ λ = 314 × 10⁻²³√(2) × 3.14 × 25 × 10⁻¹⁵ λ = 100 × 10⁻²³√(2) × 25 × 10⁻¹⁵ λ = 4 × 10⁻⁸√(2) = 2√(2) × 10⁻⁸ m
Pattern Recognition

The temperature 314 K and π ≈ 3.14 are intentionally matched to cancel out and give a factor of 100. 1.38 cancels completely. The rest is simply handling powers of 10.

Chapter Mix

Class 11 Physics: Kinetic Theory

Reference Study Guides

More Kinetic Theory Previous-Year Questions — Page 6

Q31 jee_main_2024_31_jan_morning Kinetic Energy Of Gas Molecules
The parameter that remains the same for molecules of all gases at a given temperature is :
  • A. kinetic energy
  • B. momentum
  • C. mass
  • D. speed

Solution

Related Formula
KE = (f)/(2)kT
Core Logic

The average translational kinetic energy of any gas molecule depends only on the absolute temperature of the gas and is independent of the nature or mass of the gas.

For 1 mole of any ideal gas, the average translational kinetic energy is (3)/(2)RT. Therefore, at a given temperature, the kinetic energy parameter is uniform across all ideal gases.

Pattern Recognition

Temperature is directly proportional to average translational kinetic energy. If T is constant, KE is constant for all gases regardless of mass.

Chapter Mix

Class 11 Physics: Kinetic Theory

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