Which of the following is CORRECT about the viscosity of gas?
Try it first: pick an option, then read the explanation.
Correct answer: B. Increases with an increase in the temperature
Asked in SSC JE 22.1.2018 (Morning Shift)
Detailed Explanation
The kinetic theory of gases explains how transport properties emerge from molecular motion. Thermal energy accelerates gas molecules, altering their shear-resisting behavior.
Why “Increases with an increase in the temperature” Is Correct
In gases, viscous resistance results from the transfer of momentum by molecules moving between layers of differing velocities. As temperature rises, molecular speeds increase, collision frequencies rise, and viscosity increases.
Why the Other Options Are Wrong
- A. Inversely proportional to the temperature: Gas viscosity increases with temperature, so it is not inversely proportional.
- C. Independent of pressure: While viscosity is relatively independent of pressure at moderate pressures, it is strongly dependent on temperature.
- D. Independent of temperature: Gas viscosity changes significantly with temperature, making statement (d) false.
Key Point
Gas viscosity increases with temperature: μ ∝ √T.
Key Concepts for Students
- Kinetic theory: μ ≈ (1/3) ρ v_avg λ, where v_avg ∝ √T and λ ∝ 1/ρ.
- Consequently, μ is proportional to √T and nearly independent of pressure at moderate ranges.
- Liquids behave oppositely: liquid viscosity drops sharply with increasing temperature.
Practice more: this is question 49 in Properties of Fluid MCQs – Part 4. Try the whole set and check every answer instantly.