Question

A glass capillary tube of internal radius r = 0.25mm is immersed in water. The top end of the tube is projected by 2cm above the surface of the water. At what angle does the liquid meet the tube? Surface tension of water = 0.7N/m.

• A. \( \theta = 90^\circ \)
• B. \( \theta = 70^\circ \)
• C. \( \theta = 45^\circ \)
• D. θ = 35^∘

Hint:

Capillary rise decreases as contact angle increases.

Answer 1

The Correct Option is B

Step 1: Capillary rise formula: h = (2Tcosθ)/(ρ g r)
Step 2: Given h = 2cm = 0.02m, r = 0.25×10⁻3m, T = 0.7N/m, ρ = 1000kg/m³.
Step 3: Substituting values, cosθ = (hρ g r)/(2T) ≈ 0.34 ⟹ θ ≈ 70^∘