A U-shaped wire is dipped in a soap solution, and removed. The th… - Vidyadip

Question

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

✓

Answer

The weight that the soap film supports, W = 1.5 × 10^-2N

Length of the slider, l = 30cm = 0.3m

A soap film has two free surfaces.

$\therefore$ Total length = 2l = 2 × 0.3 = 0.6m

Surface tension, $\text{S}=\frac{\text{Force of Weight}}{2\text{l}}$

$= 1.5 \times\frac{10^{-2}}{0.6}= 2.5\times10-2\text{N/m}$

Therefore, the surface tension of the film is 2.5 × 10-2N m^-1.

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