The surface of a soap film was increasedd isothermallly by `Delta o` at a temperature `T`. Knowing the surface tension of the soap water solution `alpha` and the temperature coefficient `d alpha//d T`, find the increment.
(a) of the entropy of the film's surface layer ,
(b) of the internal energy of the surface layer.

Explanation

As before we can calculate the heat required. It, is taking into account two sides of the soap film
`delta q = - T(d alpha)/(dT) delta sigma xx 2`
Thus `Delta S = (delta q)/(T) = -2 (d alpha)/(d T) delta sigma`
Now `Delta F = 2 alpha delta sigma` so, `Delta U = Delta F + T Delta S = 2 (alpha - T (d alpha)/(dT)) delta sigma`.