Physics Paper 2, Nov/Dec. 2010  
Questions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Main
General Comments

Question 5

Explain how the addition of detergents of water reduces surface tension



Very few candidates managed to render the correct explanation in terms of weakening of the cohesive/intermolecular forces among the surface molecules. Majority failed to relate surface tension to molecular properties. Performance was poor.

The expected answer is:

Surface tension is due to the intermolecular forces among the surface molecules of a liquid. Addition of detergents to water reduces/weakens theses forces; hence the reduction in its surface tension


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