NTA Abhyas JEE Main2020PhysicsMechanical Properties of FluidsPractice
The surface tension and vapour pressure of water at 20 ° C are 7.28 × 10 - 2   Nm - 1 and 2 . 33 × 10 3   Pa respectively. At this temperature, the radius of the smallest possible drop, which can form without evaporating is
Options
- A1.25 × 10 -5 m
- B6.25 × 10 -5   m
- C4.3 × 10 -5   m
- D3.4 × 10 -5   m
Correct answer
B. 6.25 × 10 -5   m
Step-by-step solution
Here, S = 7.28 × 10 - 2 N m - 1 , P = 2.33 × 10 3 P a The drop will evaporate if the water pressure is greater than the vapour pressure P As P = 2 S R where R is the radius of drop ∴ R = 2 S P = 2 × 7.28 × 10 - 2 2.33 × 10 3 = 6.25 × 10 - 5