Answer :
Capillary rise is an interesting phenomenon that occurs due to the interplay between cohesive and adhesive forces.
Adhesive and Cohesive Forces:
- Adhesive Forces are the forces of attraction between different substances, such as a liquid and the surface of a solid.
- Cohesive Forces are the forces that hold the molecules of a liquid together.
Interaction in a Capillary Tube:
- The adhesive forces between the liquid and the tube's surface are stronger than the cohesive forces within the liquid when a narrow tube, or capillary, is submerged in a liquid that wets its surface, such as water in a glass tube.
Rising Liquid:
- The adhesive forces the liquid to spread along the inner walls of the tube, pulling it upwards.
- Surface tension, due to cohesive forces, acts to reduce the liquid's surface area but allows it to rise by forming a concave meniscus.
Balancing Forces:
- The liquid keeps rising until the downward gravitational force acting on the liquid column equalizes the upward adhesive force.
- At equilibrium, the pressure difference created by the capillary rise equals the hydrostatic pressure of the liquid column.
Height of Rise:
- The height to which the liquid rises is affected by the diameter of the tube and the properties of the liquid like surface tension. A smaller tube diameter usually means a higher rise.
Role of Pressure Difference:
- The pressure inside the liquid is lower at the meniscus than at the larger body of the liquid. This pressure difference aids the rise of the liquid in the capillary.
