Question

The shape of the meniscus of water in a glass tube is different from that of mercury in a glass tube. Why?

Short answer

When water is placed in a tube, its surface acquires a concave shape because the water in the tube wets the surface of the tube and creeps up the side. Mercury does not wet glass if the tube and the cohesive forces present within the mercury drops are stronger than the adhesive forces between the drops and glass.

When water and mercury are taken in two different capillary tubes, the shape of the meniscus formed in both the fluids is concave and convex, respectively.

Step-by-step solution

Meniscus

The meniscus is the curve formed at the upper surface of a liquid close to the surface of the container or another object. The meniscus is mainly caused by surface tension.

Concave and convex meniscus

A concave meniscus occurs when the molecules of the liquid in the container are attracted to those of the container, for example, in water. A convex meniscus occurs when the attraction present between the molecules is stronger to each other than to the container, for example, mercury in the glass tube.