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 × 10–2 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 1

Length of the slider ( L) = 30cm

We know,
A soap film has two free surface , therefore total length of the film to be supported
L" = 2L = 2×30 = 60 cm

Let s is the surface tension of the soap .
Total force on the slider due to surface tension
F = S× L"
= S × (60 cm)
= S × 0.6 N

Weight Supported by slider (w) = 1.5 × 10^-2 N

In equilibrium condition,
Force due to surface tension = weight supported by slider
F = w
S × 0.6 = 1.5 × 10^-2
S = 1.5 × 10^-2/0.6
= 2.5 × 10^-2 N/m

Answer 2

this is the answer to your question