Q. A U - shaped wire is dipped in a soap solution and removed. The thin soap film formed between the wire and light slider supports a weight of . The length of the slider is . What is the surface tension of the film?

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Solution:

A soap film has two free surfaces, so the total length of the film to be supported,

Let the surface tension of the film
If the total on the slider due to surface tension,
then

In equilibrium position, the force f on the slider due to surface tension must be balanced by the weight supported by the slider
i.e.,