Question

What is capillarity? Give any two applications of it.

Answer 1

Hint: Tubes with small diameters are known as capillary. These tubes will show rise or fall of liquid when it dipped in a liquid. This is known as capillarity and it will occur due to the cohesive force between the molecules of liquid and adhesive force between the surface of the tube and the liquid.

Complete step by step answer:
Capillarity is a phenomenon, in which we can observe that the surface of the liquid is elevated or depressed when it comes into contact with a solid. This action is known as capillary action or wicking. Cohesive and adhesive forces are the reason behind this action. Adhesive forces are developed by the attractive or repulsive force between the molecules of the liquid and those of the container and cohesive forces are developed by the attractive force between the molecules of liquid. If the adhesive forces are attractive, then the liquid will rise. Otherwise the depression of liquid will happen. When these two forces are balancing the force of gravity, then liquid will be in the equilibrium position. Hence it cannot rise or fall further.

Examples are;
Movement of ground water from wet areas to the dry area
Oil rise through the wicks of lamp
Chromatography experiments
Absorption of water of trees and distribution to the various parts of it
Applications of capillarity;
Cotton dresses are preferred for the summer since they have fine pores and that will help for the capillarity action for sweat.
The absorption of ink by using a blotting paper.
Rise of oil in the wick of a lamp helps to continue the fire.

Additional information:
Capillarity rise is due to the tendency of liquids to rise in tubes of small diameter in opposition to the gravity. Capillarity fall is due to the depression of liquids in tubes of small diameter in opposition to gravity.
The capillary action arises due to the adhesive and cohesive forces. If the diameter decreases, higher will be the liquid rise.
The height of the liquid can be written as,
$$h={\displaystyle \frac{2T\cos \theta }{r\rho g}}$$, where $$T$$ is the surface tension, $$r$$ is the radius of meniscus, $$\rho$$ is the density of the liquid, $$g$$ is the acceleration due to gravity and $$\theta$$ is the contact angle made by the liquid meniscus with the capillary’s surface.
For concave meniscus, the contact angle will be acute and for convex meniscus of liquid, the contact angle will be obtuse.

Note: The meniscus forms a different shape either convex or concave. Sometimes plane meniscus also forms. If the surface tension or ratio between the cohesion to adhesion increases, then the liquid rise also increases. If the density of liquid is more, capillary rise will be less.