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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 · 2021 · Paper I

Q3(a). Surface energy when one drop is split into 125 drops

Question

A drop of water, 0.4 cm in radius, is split up into 125 tiny drops. Find the increase in surface energy. [γ_water (surface tension of water) = 72 dynes/cm]

Answer in brief

Increase in surface energy = γΔA = 72 × 8.042 = 579 erg = 5.79 × 10⁻⁵ J, as the water surface becomes five times larger.

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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 →

Coverssurface tensionsurface energysplitting of dropsGibbs surface energy

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