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A vertical glass capillary of internal diameter 0.50 mm is dipped in water such that 25 mm of the tube projects above the water surface. Taking the surface tension of water as 73 * 10⁻³ N/m, find the radius of curvature of the water meniscus inside the tube.
- R = 0.6 m
- R = 6 mm
- R = 0.6 mm
- R = 0.6 Km
Correct answer: R = 0.6 mm
Solution
If the unobstructed capillary rise would exceed the available length, water rises to the top and the meniscus flattens (its radius of curvature R increases) so that the pressure balance h = 2T/(rho*g*R) holds with h equal to the actual height above the water surface.
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