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Which of the following statement is true about capillary rise: a) The meniscus will be concave b) The meniscus will be convex c) The angle of contact will be greater than 90° d) The angle of contact will be less than 90°

Which of the following statement is true about capillary rise: a) The meniscus will be concave b) The meniscus will be convex c) The angle of contact will be greater than 90° d) The angle of contact will be less than 90° Correct Answer Both a and d are correct

CONCEPT:

  • Capillary action 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 there will be the capillary rise and the meniscus will be of concave shape.
  • If the cohesive force is more compared to adhesive force there will be capillary fall and the meniscus will be of convex shape.

EXPLANATION:

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  • If the adhesive force is more compared to cohesive force there will be the capillary rise and the meniscus will be of concave shape.
  • Since the meniscus is concave in the capillary rise, so the angle of contact will be less than 90°. Hence, option 2 is correct.

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