Surface tension vs. adhesion: Why does water spread on clean glass but mercury remains nearly spherical? Explain using cohesion (liquid–liquid) and adhesion (liquid–solid) along with surface tension.
IIT JEE
Physics
Difficulty: Easy
Choose an option
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ABecause water has higher cohesion than adhesion to glass; mercury has higher adhesion
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BBecause water adheres strongly to glass (adhesion > cohesion), while mercury's cohesion > adhesion to glass
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CBecause both have zero surface tension
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DBecause gravity is negligible for mercury
Answer
Correct Answer: Because water adheres strongly to glass (adhesion > cohesion), while mercury's cohesion > adhesion to glass
Explanation
ConceptA liquid spreads when adhesion to the surface exceeds cohesion; it beads up when cohesion dominates or surface tension is very high.
ApplicationWater–glass: strong adhesion ⇒ wetting/spreading. Mercury: very high surface tension and strong cohesion with weak adhesion to glass ⇒ spherical drops (non-wetting).
Final AnswerBecause water adheres strongly to glass (adhesion > cohesion), while mercury's cohesion > adhesion to glass