Question

Explain the phenomenon of capillarity?

Answer 1

Hint: Capillarity is a phenomenon by which the liquid moves without the help of gravity. The liquid level rises to some height against the gravitational force, through the narrow tube. This action is due to the phenomenon of surface tension of the liquid.

Complete step by step solution
The capillarity action is due to the surface tension and adhesive force between the liquid molecule and the molecule of the tube. Surface tension of the liquid is due to the cohesive attraction of the liquid molecules.

When a thin tube which is open or closed top is inserted into the container having liquid, then the liquid inside the tube gets rising to some height $h$ above the liquid in the container. Then the diameter of the tube is $D$. The density of the liquid is $\rho $. Then,
$W = \rho \times \left( {\dfrac{{\pi {D^2}}}{4}} \right) \times hg$
Where, $W$ is the weight of the liquid, $g$ is the acceleration due to gravity.

When the glass tube is dipped into the container having the liquid of angle of contact which is less than ${90^ \circ }$ then the liquid rises up in the tube till the equilibrium condition is attended. And here the adhesive forces are greater than cohesive force. Example: Water.

When the glass tube is dipped into the container having the liquid of angle of contact which is greater than ${90^ \circ }$ then the liquid gets fall off in the tube till the equilibrium condition is attended. And here the cohesive forces are greater than adhesive force. Example: Mercury.

Note: Capillarity is the ability of a liquid which flows in narrow spaces without any assistance and acts against gravity. It occurs because of the intermolecular forces between the liquid and the molecules of the narrow tube which is inserted in the container of the liquid.