Capillarity is due to: I. surface tension, II. cohesion, III. viscosity, IV. vapour pressure, V. weight density of liquid
Try it first: pick an option, then read the explanation.
Correct answer: C. I
Asked in SSC JE 2014, Morning
Detailed Explanation
Capillary rise and depression occur when a thin tube is immersed in a liquid bath. The liquid column is held by interfacial forces.
Why “I” Is Correct
Capillarity is directly caused by surface tension (item I) acting along the contact line of the meniscus. Among the options provided, (c) I is correct.
Why the Other Options Are Wrong
- A. II, III: Viscosity (III) affects only the rate of capillary rise, not the equilibrium capillary height.
- B. III: Viscosity (III) does not cause capillarity.
- D. II, III, V: Viscosity (III) and vapour pressure (IV) are not the primary causes of capillarity.
Key Point
Capillarity is caused by surface tension (acting through cohesion and adhesion).
Key Concepts for Students
- Capillary height formula: h = 4T cosθ / (ρgd).
- Surface tension T provides the upward vertical lifting force.
- Cohesion and adhesion determine the contact angle θ.
Practice more: this is question 71 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.