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Friday, 9 October

JEE Main 2020 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 9 January 2020, Shift 2, Physics Q9

Question 9 of 75 in this shift, Physics question 9 of 25, Section A.

A small spherical droplet of density dd is floating exactly half immersed in a liquid of density ρ\rho and surface tension TT. The radius of the droplet is (take note that the surface tension applies an upward force on the droplet) :
  1. (1)r=T(d−ρ)gr = \sqrt{\frac{T}{(d-\rho)g}}
  2. (2)r=3T(2d−ρ)gr = \sqrt{\frac{3T}{(2d-\rho)g}}Official answer
  3. (3)r=2T3(d+ρ)gr = \sqrt{\frac{2T}{3(d+\rho)g}}
  4. (4)r=T(d+ρ)gr = \sqrt{\frac{T}{(d+\rho)g}}

Official answer

Option 2

NTA final key (Jan 2020).

Chapter
Mechanical Properties of Fluids
Topic
Surface Tension
Idea tested
Surface Tension Force on a Floating Sphere

Same topic in other shifts

All Surface Tension questions
  1. 2 Apr 2026, Shift 1 · Q45A liquid drop of diameter 22 mm breaks into 512512 droplets. The change in surface energy is α×10−6\alpha\times10^{-6} J. The value of…EasySingle correct
  2. 2 Apr 2026, Shift 2 · Q33The surface tension of a soap bubble is 0.03 N/m. The work done in increasing the diameter of bubble from 2 cm to 6 cm is…EasySingle correct
  3. 4 Apr 2026, Shift 1 · Q47The surface tension of a soap solution is 3.5×10−23.5\times10^{-2} N/m. The work required to increase the radius of a soap bubble from 11 cm to…MediumNumerical value
  4. 5 Apr 2026, Shift 2 · Q33Eight mercury drops, each of radius rr, coalesce to form a bigger drop. The surface energy released in this process is __________. (S is…EasySingle correct
  5. 2 Apr 2025, Shift 2 · Q31Two water drops each of radius rr coalesce to form a bigger drop. If TT is the surface tension, the surface energy released in this…EasySingle correct
  6. 3 Apr 2025, Shift 2 · Q47The excess pressure inside a soap bubble A in air is half the excess pressure inside another soap bubble B in air. If the volume of the…EasyNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.