Question

It is difficult to fill a capillary tube with mercury than with water since:

• A. Angle of contact between glass & mercury is more than 90${}^o$ and the angle of contact between glass and water is less than 90${}^o$.
• B. Angle of contact is between glass and mercury is less than 90${}^o$ and the angle of contact between glass and water is more than 90${}^o$.
• C. Angle of contact is same for both water and mercury.
• D. Mercury is less dense than water.

Answer 1

The correct option is A Angle of contact between glass & mercury is more than 90${}^o$ and the angle of contact between glass and water is less than 90${}^o$.

Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules. For mercury, cohesive force between wall of capillary tube and mercury molecules is stronger hence, angle of contact between glass & mercury is more than ${90}^{\circ }$. And adhesive force between wall of capillary tube and water molecules is stronger hence, the angle of contact between glass and water is less than ${90}^{\circ }$. Hence, it is difficult to fill a capillary tube with mercury than with water.