Question

The angle of contact at the interface of water glass is $0{}^\circ$, Ethyl-alcohol glass is $0{}^\circ$, Mercury glass is $140{}^\circ$ and Methyl iodide is $30{}^\circ$. A glass capillary is put in a trough containing one of these for liquids it is observed that the meniscus is convex. The liquid in the trough is:
(A) Water
(B) Ethyl alcohol
(C) Mercury
(D) Methyl alcohol

Answer 1

Hint: We know that a capillary tube is nothing but a long, fixed-length tube with a very small diameter that is installed between the condenser and the evaporator. The capillary tube actually meters the refrigerant from the condenser to the evaporator. Capillary tube is designed to change the high-pressure liquid refrigerant into a low-pressure spray of refrigerant. The amount of pressure drop is dependent on the length and inside diameter of the capillary tube.

Complete step-by step answer:
At first let us describe a few terms that are mentioned in the question.
We know that the meniscus is the curve in the upper surface of a liquid close to the surface of the container or another object, caused by surface tension. It can be either concave or convex, depending on the liquid and the surface.
It should also be known to us that a convex meniscus occurs when the molecules have a stronger attraction to each other than to the container, as with mercury and glass. A flat meniscus occurs with water in some types of plastic tubes; tubes made out of material that water does not stick to.
The meniscus of liquid in a capillary tube will be convex upwards if the angle of contract is obtuse. It is so when one end of a glass capillary tube is immersed in a trough of mercury.
Hence the liquid in the trough is Mercury.

Hence, the correct answer is Option C.

Note: We should know that mercury does not wet glass; the cohesive forces within the drops are stronger than the adhesive forces between the drops and glass. When liquid mercury is confined in a tube, its surface (meniscus) has a convex shape because the cohesive forces in liquid mercury tend to draw it into a drop. A meniscus occurs because of surface tension in the liquid and must be read at eye level. For a concave meniscus, the correct volume will be read at the bottom of the curve. For a convex meniscus, the opposite is true and the correct reading will be at the top of the curve.