What is the effect of a closed capillary tube on capillary rise compared to an open tube?

• A. Capillary rise is lower in a closed tube due to pressure.
• B. Capillary rise is higher in a closed tube.
• C. Capillary rise is the same as open.
• D. Capillary rise is zero in a closed tube.

Answer: (A)

Capillary rise depends on the balance between the capillary pressure pulling the liquid up the tube and the hydrostatic weight of the liquid column. In an open tube, the top surface is exposed to atmospheric pressure, so the rise stops when ρgh equals the capillary pressure, giving the typical rise height formula. When the tube is closed at the top, the space above the liquid traps gas. As the liquid climbs, this trapped gas is compressed, raising its pressure and adding resistance to further rise. That extra pressure reduces the net upward push, so the liquid cannot rise as high as it does in an open tube. So the capillary rise is lower in a closed tube due to the pressure from the compressed trapped gas.