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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper I

Q4(b). Pressure difference needed to drink through a tilted straw

Question

A 15 cm drinking straw is inserted in a glass of water at an angle of 45°. What pressure difference (in torr) must be generated across the length of the straw to drink water? The density of water is 1.0 g cm⁻³.

Answer in brief

ΔP = ρgl sin 45° = 1.04 × 10³ Pa = 7.8 torr.

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Topic notes: the liquid state: surface tension, the Kelvin equation, capillary action, viscosity and liquid crystals, with every Civil Services, IFoS and Geo-Scientist PYQ →

Covershydrostatic pressureρghtorr conversiondrinking strawmanometer

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