Question

Water rises in glass capillary tube due to:
A. Surface tension of water.
B. Cohesive force of glass molecules.
C. Temperature of water.
D. Adhesive force between the water molecule and the walls of the glass tube

Answer 1

Hint: Force exerted on the wall by the water is due to the surface tension of the water molecule. Water in the capillary tube is attracted to the wall of the capillary tube. Water molecules are applying force in every direction.

Complete step by step answer:
Water acts as a binding force and attractive force, this force is called surface tension. Surface tension is measured as the energy required by one unit of area to increase the surface area of a liquid. The surface tension of a liquid is the result of an unbalance of attractive intermolecular forces, the cohesive forces between molecules.

Consider the $l$ is the diameter of the capillary tube. If F is the total force on either side of the diameter then we can write,

$\begin{array}{c}F \propto l\\F = \sigma l\\\sigma = \dfrac{F}{l}\\{\rm{Surface}}\,{\rm{tension}}\,{\rm{ = }}\,\dfrac{{{\rm{Force}}}}{{{\rm{Length}}}}\end{array}$

Surface tension is measured as the force acting per unit length of an imaginary line considered on the liquid surface, the direction of force perpendicular to this line, and tangential to the liquid surface.
Because of surface tension (cohesive force inside the liquid), the water rises against gravity in the small glass capillary. This phenomenon is known as 'capillary action.'

Thus, the correct option is A.

Note: The unbalanced attraction of molecules on a liquid’s surface tends to pull the molecules back into the bulk liquid leaving the surface with the minimum number of molecules. It required energy to increase a liquid's surface area because, in the unbalanced situation, a larger surface area contains more molecules.