With increase in temperature the viscosity of air and water varies as?
Try it first: pick an option, then read the explanation.
Correct answer: D. Viscosity of air increases and viscosity of water decreases
Asked in SSC JE 2016
Detailed Explanation
Temperature affects gases and liquids in fundamentally opposite ways because their dominant mechanisms of viscous shear resistance differ.
Why “Viscosity of air increases and viscosity of water decreases” Is Correct
For air (a gas), higher temperatures intensify molecular momentum exchange, increasing viscosity. For water (a liquid), higher temperatures weaken cohesive bonding, decreasing viscosity.
Why the Other Options Are Wrong
- A. Viscosity of air increases and viscosity of water increases: Water viscosity decreases with temperature, so both cannot increase.
- B. Viscosity of air decreases and viscosity of water decreases: Air viscosity increases with temperature, so both cannot decrease.
- C. Viscosity of air decreases and viscosity of water increases: This statement reverses the behavior of both air and water.
Key Point
With increasing temperature: gas viscosity increases; liquid viscosity decreases.
Key Concepts for Students
- Gas viscosity μ ∝ √T (momentum transfer).
- Liquid viscosity μ ∝ exp(E / RT) (cohesive activation energy).
- Hot engine oil flows much more easily than cold oil.
Practice more: this is question 70 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.