# Capillarity in Physics | Definition, Formula, Examples – Surface Tension

Capillarity Definition Physics:
The phenomenon of rise or fall of liquid column in a capillary tube is called capillarity.

We are giving a detailed and clear sheet on all Physics Notes that are very useful to understand the Basic Physics Concepts.

## Capillarity in Physics | Definition, Formula, Examples – Surface Tension

Ascent of a liquid column in a capillary tube is given by

h = $$\frac{2 S \cos \theta}{r \rho g}-\frac{r}{3}$$

Capillarity Formula Derivation:
If capillary is very narrow, then

h = $$\frac{2 S \cos \theta}{r \rho g}$$

where,
r = radius of capillary tube,
ρ = density of the liquid,
θ = angle of contact and
S = surface tension of liquid.

• If θ < 90°, cos θ is positive, so h is positive, i.e. liquid rises in a capillary tube.
• If θ > 90°, cos θ is negative, so h is negative, i.e. liquid falls in a capillary tube.
• Rise of liquid in a capillary tube does not violate law of conservation of energy.

Capillarity Examples in Daily Life:
(i) The kerosene oil in a lantern and the melted wax in a candle, rise in the capillaries formed in the cotton wick and burns.

(ii) Coffee powder is easily soluble in water because water immediately wets the fine granules of coffee by the action of capillarity.

(iii) The water given to the fields rises in the innumerable capillaries formed in the stems of plants and trees and reaches the leaves.

(iv) The tip of nib of a pen is split to provide capillary action for the ink to rise.

(v) The action of a towel in soaking up moisture from the body is due to the capillary action of cotton in the towel.

Surface Tension:
In Physics, the tension of the surface film of a liquid because of the attraction of the surface particles by the bulk of the liquid, which tries to minimize surface area is called surface tension. When the surface of the liquid is strong enough, then surface tension is applicable. It is strong enough to hold weight.