JEE Advanced2018PhysicsMechanical Properties of FluidsActual
A uniform capillary tube of inner radius r is dipped vertically into a beaker filled with water. The water rises to a height h in the capillary tube above the water surface in the beaker. The surface tension of water is σ . The angle of contact between water and the wall of the capillary tube is θ . Ignore the mass of water in the meniscus. Which of the following statements is (are) true?
Options
- AFor a given material of the capillary tube, h decreases with increase in r
- BFor a given material of the capillary tube, h is independent of σ
- CIf this experiment is performed in a lift going up with a constant acceleration, then h decreases
- Dh is proportional to contact angle θ
Correct answer
A. For a given material of the capillary tube, h decreases with increase in r
Step-by-step solution
2 σ R = ρ g h R → R a d i u s o f m e n i s c u s h = 2 σ R ρ g R = r cos θ [r→radius of capillary; θ → contact angle] h = 2 σ cos θ r ρ g ( A ) For given material, θ = c o n s t a n t h ∝ 1 r ( B ) h depends on σ ( C ) If lift is going up with constant acceleration, g e f f = g + a h = 2 σ cos θ r ρ g + a It means h decreases ( D ) h is proportional to cos θ , N o t θ