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A capillary tube of radius 0.50 mm stands vertically in a bowl of water. Determine the gauge pressure (difference from atmospheric pressure) of the water inside the tube at a depth of 5.0 cm below the surface. Surface tension of water = 0.075 N/m. (Take g = 10 m/s², density of water = 1000 kg/m³.)
- 100 Pa
- 150 Pa
- 160 Pa
- 190 Pa
Correct answer: 190 Pa
Solution
Just under the curved meniscus the pressure is P0 - 2T/r. Moving down by h the pressure increases by rho*g*h. The gauge pressure is the net difference from atmospheric.
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