question_answer 17)

A U-shaped wire is dipped in a soap solution, and removed. A thin soap film formed between the wire and a light slider supports a eight of \[1.5\times {{10}^{-2}}\,N\] (which includes the small weight of the slider). The length of the slider is 30 cm. What is the surface tension of the film?

Answer:

We know that soap film has two free surfaces, so total length of the film to be supported, \[=2l=2\times 30=60\,cm=0.6\,m\] Total force on the slider due to surface tension will be, \[19\cdot 1\]. In equilibrium position, the force F on slider due to surface tension must balance the weight mg \[42\times {{10}^{9}}N{{m}^{-2}}.\]i.e., \[A=15\cdot 2\times 19\cdot 2\times {{10}^{-6}}{{m}^{2}};\] Or \[F=44,500N;G=42\times {{10}^{9}}N{{m}^{-2}}\]