A U-shaped wire is dipped in a soap solution, and removed. The thin soap film formed between the wir

Question

A U-shaped wire is dipped in a soap solution, and removed. The thin soap film formed between the wire and a light slider supports a total weight of $1.5 	imes 10^{-2}	ext{ N}$. The length of the slider is $30	ext{ cm}$. What is the surface tension of the film?

Professor PC Thomas Classes · Answer

A soap film in air has two distinct liquid-air surfaces. The total upward surface tension force is $2 S L$. In equilibrium, $2 S L = W \implies S = \frac{W}{2L} = \frac{1.5 	imes 10^{-2}}{2 	imes 0.30} = 2.5 	imes 10^{-2}	ext{ N/m} = 0.025	ext{ N/m}$.