The surface of a liquid acts like a stretched elastic membrane under tension. This is mainly due to:
Try it first: pick an option, then read the explanation.
Correct answer: C. surface tension
Asked in SSC JE 14.11.2022
Detailed Explanation
Molecules inside a liquid are surrounded by neighbors and experience symmetrical cohesive attractions. Surface molecules experience a net inward cohesive pull, creating an interfacial tension across the free boundary.
Why “surface tension” Is Correct
Due to surface tension, the surface layer of liquid contracts to the smallest possible surface area and behaves mechanically like a taut, stretched elastic membrane supporting transverse loads.
Why the Other Options Are Wrong
- A. viscosity: Viscosity resists shearing motion between adjacent layers, not interfacial surface contraction.
- B. velocity of flow: Velocity of flow describes motion kinematics and is unrelated to static surface tension phenomena.
- D. capillarity: Capillarity is a secondary consequence of surface tension occurring at confined solid boundaries.
Key Point
Surface tension causes a free liquid boundary to behave as a stretched elastic membrane.
Key Concepts for Students
- Surface tension force acts in the plane of the interface normal to any line.
- Unbalanced cohesive intermolecular forces pull surface molecules inward.
- Surface tension enables small insects (like water striders) to walk on water.
Practice more: this is question 24 in Properties of Fluid MCQs – Part 2. Try the whole set and check every answer instantly.