UPSC Prelims 2012 · Question 93 of 98

UPSC Prelims 2012 question on Capillarity Applications

Consider the following statements:

If there were no phenomenon of capillarity

1. It would be difficult to use a kerosene lamp.

2. One would not be able to use a straw to consume a soft drink.

3. The blotting paper would fail to function.

4. The big trees that we see around would not have grown on the Earth.

Which of the statements given above are correct?

  1. 1, 2 and 3 only
  2. 1, 3 and 4 only
  3. 2 and 4 only
  4. 1, 2, 3 and 4
Show answer

Answer: B. 1, 3 and 4 only

Verdict

Correct Answer: 1, 3 and 4 only

Statements 1, 3 and 4 are correct because kerosene lamps, blotting paper and plant water transport depend on capillarity, while drinking through a straw depends on atmospheric pressure.

Analysis

Capillarity is the ability of a liquid to rise or move through narrow spaces due to adhesive and cohesive forces.

It explains the movement of liquid through wicks, paper fibres and fine tubes, even against gravity.

Statement by statement

1. It would be difficult to use a kerosene lamp — Correct

In a kerosene lamp, kerosene rises through the wick due to capillary action.

Without capillarity, the fuel would not move properly from the container to the flame.

2. One would not be able to use a straw to consume a soft drink — Incorrect

Drinking through a straw is not based on capillarity.

It works because sucking reduces pressure inside the straw, and atmospheric pressure pushes the liquid upward.

This is a pressure difference phenomenon, not capillary action.

3. The blotting paper would fail to function — Correct

Blotting paper absorbs ink or water through tiny spaces between its fibres.

This absorption happens due to capillary action.

Without capillarity, blotting paper would not absorb liquid effectively.

4. The big trees that we see around would not have grown on the Earth — Correct

Capillary action helps in the upward movement of water through narrow vessels in plants.

It assists in transporting water and dissolved minerals from roots to higher parts of the plant.

Without capillarity, water transport in tall plants would become difficult.

Extra UPSC info

* Capillarity depends on adhesion, cohesion and surface tension.

* Water rises in a narrow tube when adhesive force is greater than cohesive force.

* Mercury shows capillary depression because cohesive force is greater than adhesive force.

* Capillary action is seen in soil water movement, plant water transport, towels, sponges and ink absorption.

* Do not confuse capillarity with pressure difference; straw drinking works mainly due to atmospheric pressure.

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