Sample 1Medium
Water rises in a clean glass capillary of radius 0.14 mm. Take surface tension 0.07 N m⁻¹, angle of contact 0°, density 1000 kg m⁻³ and g = 10 m s⁻². The height to which water rises is
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The answer is C.
h = 2S cos θ/(rρg) = (2 × 0.07 × 1)/(1.4 × 10⁻⁴ × 1000 × 10) = 0.14/1.4 = 0.1 m = 10 cm.
- A.
5 cm drops the factor 2 in h = 2S cos θ/(rρg).
- B.
20 cm would follow from a radius of 0.07 mm; with r = 0.14 mm the rise is 0.1 m.
- D.
1 cm is ten times too small, from mis-converting 0.14 mm.
NCERT: Class 11 Physics, Chapter 9, Surface tension (capillary rise)