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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 weight of `1.5xx10^(-2)N` (which includes the small weigh of the slider). The length of the slider is 30cm. 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 = 2xx30=60cm =0.6m` Total force on the slider due to surface tension will be , `F = S xx 2l = S xx 0.6N` In equilibrium position, the force F on slider due to surface tension must balance the weight mg `(=1.5xx10^(2)N)` , i.e, `F=1.5xx10^(-2) = Sxx0.6 or S=(1.5xx10^(-2))/(0.5) = 2.5 xx 10^(-2)Nm^(-1)`. |
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