GATE 2026 PI – Question 43
A vertical glass tube of diameter 2.5 mm is immersed in a fluid with zero contact angle, surface tension 0.1 N/m, density 1000 kg/m³ and g = 10 m/s². Find approximate capillary rise (mm).
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Correct answer: (C) 16
Explanation
Balance the vertical surface-tension force with column weight: $\pi d\sigma\cos\theta=\rho g(\pi d^2/4)h$. Hence $h=4\sigma\cos\theta/(\rho gd)=4(0.1)/(1000\cdot10\cdot0.0025)=0.016$ m = **16 mm, C**.