Which factors affect capillary action?

• A. The size of the capillary tube; open/closed conditions affect rise.
• B. The color of the liquid.
• C. The ambient humidity alone.
• D. The amount of liquid.

Answer: (A)

Capillary action is driven by the balance of adhesive forces between the liquid and the tube and the cohesive forces inside the liquid, along with the pressure at the liquid surface. The height the liquid climbs in a capillary mainly depends on the tube’s radius and the pressure conditions above the liquid. A smaller tube radius increases the rise because the curvature at the meniscus is steeper, and whether the space above the liquid is open to air or sealed can change the pressure environment and thus the rise. The color of the liquid, ambient humidity, or the total amount of liquid do not determine how high capillary rise occurs under normal conditions.