Surface tension:
Try it first: pick an option, then read the explanation.
Correct answer: A. Acts in the plane of interface normal to any line in the surface
Asked in SSC JE 1 MARCH 2017 Morning Shift
Detailed Explanation
Surface tension is a thermodynamic property of liquid interfaces caused by unbalanced cohesive attractions. Mechanically, it behaves as a uniform tensile stress across the boundary.
Why “Acts in the plane of interface normal to any line in the surface” Is Correct
By definition, surface tension force acts tangentially within the plane of the interface and perpendicular to any imaginary line drawn on that interface.
Why the Other Options Are Wrong
- B. Is also known as capillarity: Capillarity is a phenomenon resulting from the combined effect of surface tension, adhesion, and cohesion in narrow tubes, not a synonym for surface tension.
- C. Is a function of the curvature of the interface: Surface tension is an intrinsic property of the fluid pair and temperature, independent of interfacial curvature.
- D. Decreases with fall in temperature: Surface tension decreases with a rise in temperature, not a fall (it increases as temperature drops).
Key Point
Surface tension acts in the plane of the interface perpendicular to any line in the surface.
Key Concepts for Students
- Surface tension decreases with increasing temperature, reaching zero at the critical point.
- Interfacial tension exists between two immiscible liquids (e.g. oil and water).
- Young-Laplace equation relates pressure difference to surface tension and curvature.
Practice more: this is question 66 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.