A capillary tube of radius 1 mm, open at both ends, is filled completely with water and held vertically. What length of water column remains in the tube? (Surface tension of water = 73.5 * 10⁻³ N/m, contact angle = 0 deg, g = 9.8 m/s²)

0.3 cm
3 cm
6 cm
0.03 cm

Correct answer: 3 cm

Solution

A tube open at both ends develops two menisci, so the surface tension support is doubled compared with a normal capillary rise, retaining a column of height 4T/(r*rho*g).

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