Surface Tension :
The property of a liquid due to which its free surface tries to have minimum surface area is called surface tension. A small liquid drop has spherical shape due to surface tension. Surface tension of a liquid is measured by the force acting per unit length on either side of an imaginary line drawn on the free surface of liquid, then T = (F/L).
(1) It depends only on the nature of liquid and is independent of the area of surface or length of line considered.
(2) It is a scalar as it has a unique direction which is not to be specified.
(3) Dimension : [MT–2]. (Similar to force constant)
(4) Units : N/m (S.I.) and Dyne/cm [C.G.S.]
Surface Energy :
The potential energy of surface molecules per unit area of the surface is called surface energy.
Unit : Joule/m2 (S.I.) erg/cm2 (C.G.S.)
Dimension : [MT–2]
∴ W = T × ∆A [∆A = Total increases in area of the film from both the sides]
i.e., surface tension may be defined as the amount of work done in increasing the area of the liquid surface by unity against the force of surface tension at constant temperature.