Capillary Action in Physics:
The word ‘capillary‘ has originated from capillus. It is a Latin word that means ‘hair‘. So, a tube with uniform fine small-bore-like hair is known as a capillary tube.
When a capillary tube is inserted vertically upright into the water, the water rises within the tube and its level inside the tube stands higher than the water level outside. Moreover, the surface of the water inside the tube takes a concave shape instead of a horizontal one.
Liquids like water, alcohol, copper sulfate solution, etc can wet glass. If a capillary tube made of glass is dipped into these liquids, then the same phenomenon occurs. On the other hand, if a capillary glass tube is dipped into mercury, then the level of mercury in the tube falls slightly. The mercury stands at a lower level inside the capillary tube than that outside it. Moreover, the upper meniscus of mercury takes a convex shape.
The narrower the bore of the capillary tube, the greater the ascent or descent of the liquid level. This type of rise or fall of a liquid in a capillary tube is called capillary action.