UPSC Prelims 2012 · GS Paper I
Question 93: Science and Technology
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?
AnswerUPSC’s answer is (b).
Capillarity is the rise of liquid in narrow tubes or pores. It lets kerosene climb a lamp wick, blotting paper soak up ink, and water rise through the narrow vessels of tall trees (along with transpiration pull). Drinking through a straw works by atmospheric pressure pushing the liquid up when pressure in the mouth is reduced, not by capillarity.
- 1. A kerosene lamp wick draws the fuel up by capillarity.
- 2. A straw works by atmospheric pressure, not capillarity.
- 3. Blotting paper absorbs ink by capillary action.
- 4. Water rises through the narrow vessels of tall trees partly by capillarity.
How you could have got this
- If you were sure statement 2 is not correct, (a), (c) and (d) go: each of them includes 2.
What you needed to know: A straw works by atmospheric pressure, not capillarity.
Only (b) is left. You didn’t need statements 1, 3 or 4.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Wrong: it includes drinking through a straw, which depends on atmospheric pressure.
- (b) Correct: lamp wick, blotting paper and tall trees depend on capillarity.
- (c) Wrong: straw drinking is not capillarity, and it leaves out the lamp and blotting paper.
- (d) Wrong: statement 2 on straws is false.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper I, Series A. The paper on upsc.gov.in.