Due to stronger cohesive than adhesive forces mercury levels falls in a capillary tube. However, water level rises in a capillary tube due to greater adhesive than cohesive forces.
Capillary action refers to the rise or fall of a liquid in a narrow tube.
The height to which a liquid is depressed or rises in a narrow tube depends on the strength of the cohesive forces of the molecules of the fluid compared to the adhesive forces between the molecules of the fluid and the walls of the tube.
In water, the adhesive forces between the walls of the tube and water molecules is greater than the cohesive forces between water molecules, hence water rises in a capillary tube.
In mercury the adhesive forces between the walls of the tube and water molecules is less than the cohesive forces between mercury molecules, hence mercury levels falls in a capillary tube.
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