Question

The angle of contact between glass and mercury is :
A. ${{0}^{0}}$
B. ${{30}^{0}}$
C. ${{90}^{0}}$
D. ${{135}^{0}}$

Answer 1

Hint: Before starting this question, we should know the concept of “Fluid”. Anything that can flow is a fluid. Fluids include all liquids and gases. Fluid pressure is the normal force applied to a unit area of a fluid's surface.

Complete step by step solution:
Surface Tension: It is explained as the force per unit length operating perpendicularly on either side of a fictitious line placed on the liquid's free surface.
$S=\dfrac{F}{l}$
The effort needed to grow a liquid film's unit area is another definition of surface tension.
Its dimensions are $[M{{L}^{0}}{{T}^{-2}}]$ and its SI unit is N/m or $J/m^2$.

Due to surface tension, the liquid surface always gains the least amount of surface area. Thus, a liquid's smallest droplet is always spherical. As surface tension is caused by "cohesion" between a liquid's molecules, it is a molecular phenomenon. Cohesive force is the term used to describe the attraction between molecules of the same substance, and adhesive force is used to describe the attraction between molecules of different substances.

The molecular range is the furthest point ($10^{-9}\,m$) at which molecules are attracted to one another. While most liquids see a decrease in surface tension as the temperature rises, molten Cadmium and Copper experience an increase.

Angle of contact: Angle of contact is the angle between the tangent to the solid surface and the tangent to the liquid surface at the point of contact (inside the liquid).

Pair of Surface	Angle of contact
Pure water and glass	${{0}^{0}}$
Silver and glass	${{90}^{0}}$
Alcohol and glass	${{138}^{0}}$
Normal water and glass	${{8}^{0}}$
Mercury and glass	${{135}^{0}}$

Mercury and glass come into contact at an angle of 135 degrees.

Hence, the option D is correct.

Note: The angle of contact is an obtuse angle (θ > 90°) for any liquids that depress in a capillary tube but do not wet a solid surface, such as glass and mercury. The angle of contact is sharp (θ< 90°) for all liquids that moisten the solid surface and rise up in a capillary tube, such as water and glass.