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)
If T is the force due to surface tension per unit length, then F = T x 2/
W = F x = (T 2I) x = T (2Ix) = T ∆A
∴ W = T ∆A [∆A = Total increase in area of the film]
If temperature of the film remains constant in this process, this work done is stored in the film as its surface energy.
From the above expression T = W∆A or T = W [If ∆A = 1]