On increasing the temperature of a liquid, the viscosity of the liquid:
Try it first: pick an option, then read the explanation.
Correct answer: A. Decrease
Asked in SSC JE 27-01-2018 (Evening Shift)
Detailed Explanation
Viscosity in liquids originates primarily from intermolecular cohesive forces holding adjacent molecules together. Supplying thermal energy alters these intermolecular bonds.
Why “Decrease” Is Correct
As temperature increases, molecular kinetic energy overcomes cohesive bonding forces between liquid molecules, reducing their resistance to relative motion and causing viscosity to decrease.
Why the Other Options Are Wrong
- B. Increase: Viscosity increases with temperature in gases, not liquids.
- C. First decrease and then increase: Viscosity of liquids decreases monotonically with temperature across liquid phase ranges.
- D. Remains same: Liquid viscosity is strongly temperature-dependent, dropping significantly with heat.
Key Point
Liquid viscosity decreases with temperature (cohesion weakens); gas viscosity increases (momentum transfer rises).
Key Concepts for Students
- In liquids, cohesive forces dominate viscosity.
- In gases, molecular momentum exchange dominates viscosity.
- Viscosity of water drops from 1.79 cP at 0°C to 0.28 cP at 100°C.
Practice more: this is question 35 in Properties of Fluid MCQs – Part 3. Try the whole set and check every answer instantly.