Which of the following statement is correct for capillary action? (θ = angle of contact)

Question

Question

Answer 1

CONCEPT:

Capillary action:

It is the ability of a fluid to flow through a narrow space without the application of an external force.
- When a tube of very small diameter is dipped inside a fluid, we can see either a rise or a fall of fluid inside a tube.
- If the fluid level increases in the tube it is called capillary rise and if the fluid level decreases it is called capillary fall.
The reason for the capillary action is adhesive and cohesive forces.

Cohesive force	Adhesive force
The force of attraction between molecules of the same substance is called the force of cohesion. This force is lesser in liquids and least in gases.	The force of attraction between the molecules of the different substances is called the force of adhesion.
Real-life example: It is difficult to break a drop of mercury into small droplets because of the large cohesive force between the mercury molecules.	Real-life example: Adhesive force enables us to write on the blackboard with chalk.

If the adhesive force is more compared to cohesive force, then there will be the capillary rise and the meniscus will be of concave shape.
If the cohesive force is more compared to adhesive force, then there will be capillary fall and the meniscus will be of convex shape.
For capillary rise the angle of contact is less than 90° and for capillary fall the angle of contact is greater than 90°.

F1 Krupalu Ravi 29.12.21 D1

EXPLANATION:

As we know that if the adhesive force is more compared to cohesive force, then there will be the capillary rise and the meniscus will be of concave shape.
So the angle of contact is less than 90° for the capillary rise.
If the cohesive force is more compared to adhesive force, then there will be capillary fall and the meniscus will be of convex shape.
So the angle of contact is greater than 90° for capillary fall. Hence, option 1 is correct.