UPSC Prelims 1997 · General Studies
Question 106: Science and Technology
The tendency of a liquid drop to contract and occupy minimum area is due to
AnswerThe answer is (b).
Surface tension is the force along the surface of a liquid that makes the surface behave like a stretched skin. Molecules at the surface are pulled inwards by those below, so the liquid tends to take the shape with the least surface area. For a given volume that is a sphere, which is why small drops and bubbles are round. Viscosity is resistance to flow, and density is mass per unit volume.
Why each option is right or wrong
- (a) Viscosity is a liquid's resistance to flow.
- (b) Right: surface tension pulls a drop into the shape of least surface area.
- (c) Density is mass per unit volume and does not shape a drop.
- (d) Vapour pressure is the pressure of the vapour above a liquid.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1997, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.