Question

Explain surface tension on the basis of molecular theory.

Answer 1

Surface tension:

The phenomenon of surface tension can be explained by the molecular theory of matter

1. There exist cohesive forces of attraction between molecules of the liquid.
2. Inside the liquid, these forces average out and produce a net-zero effect.
3. The diagram given below shows the forces acting on molecules on the surface of the water.

1. Since the inner molecules are accompanied by identical molecules, the overall force on a single molecule is exactly zero. Molecules near the surface experience an inward force owing to strong cohesive forces, while those located within the liquid sense an outward force due to strong cohesive forces.
2. Surface molecules, on the other hand, experience inward force, making them less stable and having larger potential energy.
3. This force per unit length is called surface tension.

Mathematical representation:

$T=\frac{F}{L}$

Here,

F is the force on the object placed on the surface.

L is the length on which force acts.