A capillary tube made of glass of radius 0.15 mm is dipped vertically… | JEE Main 2020 (2 Sep, Shift 2)

Q56JEE Main 2020 · 2 SEP · SHIFT 2Medium

Angle of Contact & Capillarity

A capillary tube made of glass of radius 0.15 mm is dipped vertically in a beaker filled with methylene iodide (surface tension = 0.05 Nm–1, density = 667 kg m–3) which rises to height h in the tube. It is observed that the two tangents drawn from liquid-glass interfaces (from opp. sides of the capillary) make an angle of 60° with one another. Then h is close to (g = 10 ms–2)

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Answer: (b)

Each tangent makes the contact angle $\theta$ with the vertical wall; the two tangents meet at $2\theta = 60^\circ$ , so $\theta = 30^\circ$ .
$h = \frac{2T\cos\theta}{r\rho g} = \frac{2 \times 0.05 \times 0.866}{0.15\times10^{-3} \times 667 \times 10}$
$h = \frac{0.0866}{1.0} \approx 0.087\text{ m}$
So the answer is (b) $0.087\text{ m}$ .

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Angle of Contact & Capillarity question from JEE Main 2020 (2 Sep, Shift 2)

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