Engineering
Physics
Acceleration
Surface Tension and Surface Energy
Capillary and Pressure Difference due to Surface Tension
Question

A long capillary tube is inserted in water vertically. Water rises to a certain length of the tube. If we want to increase the length for which water will rise, we can 

raise the temperature of water.

mix some soap solution in water

Place the whole apparatus in an elevator accelerating downwards.

tilt the tube by a small angle.

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Solution
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Water rises in a capillary tube due to surface tension and the adhesive force between water and the glass wall. The height h is given by Jurin's law: h=2γcosθρgr, where γ is surface tension, θ is the contact angle, ρ is density, g is gravity, and r is the tube radius. To increase h, we must decrease the effective gravity. Placing the apparatus in a downward-accelerating elevator reduces the net downward acceleration, thus increasing the height.

Final answer: Place the whole apparatus in an elevator accelerating downwards.