VKC ScienceChemistry for written exams Telegram

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(c). Diameter of a capillary from the pressure needed to blow a bubble

Question

A capillary tube of radius r is inserted into a liquid to blow a bubble of the same radius r. If the excess pressure required to blow the bubble is 2.16 torr, what is the diameter of the capillary tube in cm? The surface tension of the liquid is 0.072 N m⁻¹.

Answer in brief

r = 2γ/ΔP = 5.0 × 10⁻⁴ m, so the diameter = 0.10 cm.

Part of VKC Basic

Read the key points and the full model answer with VKC Basic

VKC Basic (₹999 for 6 months) opens every solved answer, the notes, the handbook and the daily answer archive. Every Mains test series includes it.

See what is included Already a member? Sign in

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

The handwritten model answer pages open with the VKC plan.
Read the whole 2023 solution2023 question paper

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 →

CoversLaplace equationexcess pressuresurface tensionmaximum bubble pressure methodcapillary

All parts of Question 4