Surface Tension & Capillarity — A/L Physics

How do I practise Surface Tension & Capillarity?

1 question with a worked solution

1. A clean narrow glass capillary tube of internal radius r = 0.50 mm is dipped vertically into water of surface tension T = 0.070 N m⁻¹ and density ρ = 1000 kg m⁻³. If the contact angle is θ = 0° and g = 10 m s⁻², what height h does the water column rise in the tube?
   1. A) 5.6 cm (0.056 m)
   2. B) 1.4 cm (0.014 m)
   3. C) 7.0 cm (0.070 m)
   4. D) 2.8 cm (0.028 m)
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   Correct answer: D) 2.8 cm (0.028 m)

   From the capillary rise equation: h = (2 T cos θ) / (r ρ g). With r = 0.50 × 10⁻³ m, cos 0° = 1: h = (2 × 0.070 N m⁻¹ × 1) / (0.50 × 10⁻³ m × 1000 kg m⁻³ × 10 m s⁻²) = 0.140 / 5.0 = 0.028 m = 2.8 cm.

   Show worked solution

   Step 1: Formula: h = (2·T·cos θ) / (r·ρ·g). Step 2: h = (2 × 0.070 × 1) / (5.0 × 10⁻⁴ × 10⁴) = 0.14 / 5.0 = 0.028 m = 2.8 cm. Answer: 2.8 cm (0.028 m).
   Modelled on: the A/L Physics examination pattern

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Where does Surface Tension & Capillarity fit in the syllabus?

Unit 10.4 · Year 2 · Term 3