A liquid would wet the solid, if adhesion forces as compared to cohesion force are:
Try it first: pick an option, then read the explanation.
Correct answer: B. More
Asked in SSC JE 4 MARCH 2017 Morning Shift
Detailed Explanation
Wetting behavior on a solid surface is determined by the balance between adhesive forces (attraction between unlike molecules) and cohesive forces (attraction between like molecules).
Why “More” Is Correct
When adhesion is stronger than cohesion (adhesion > cohesion), liquid molecules are drawn toward the solid wall, causing the liquid to spread across the surface, form an acute contact angle (θ < 90°), and wet the solid.
Why the Other Options Are Wrong
- A. Less: If adhesion is less than cohesion, the liquid balls up and does not wet the solid (e.g. mercury on glass).
- C. Equal: If adhesion equals cohesion, the contact angle is 90° and the surface is neutrally wet.
- D. Less at low temperature and more at high temperature: Wetting fundamentally depends on adhesion exceeding cohesion across all temperatures where wetting occurs.
Key Point
Wetting occurs when Adhesion > Cohesion (contact angle θ < 90°, concave meniscus).
Key Concepts for Students
- Water wets clean glass (θ ≈ 0°) because adhesion between water and glass exceeds cohesion of water.
- Mercury does not wet glass (θ ≈ 130°) because cohesion of mercury exceeds adhesion with glass.
- Surfactants lower cohesive surface tension to promote wetting.
Practice more: this is question 59 in Properties of Fluid MCQs – Part 4. Try the whole set and check every answer instantly.