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

The weight that the soap film supports, W = 1.5 × 10–2 N
Length of the slider, l = 30 cm = 0.3 m
A soap film has two free surfaces.
∴ Total length = 2l = 2 × 0.3 = 0.6 m
Surface tension, S = Force or Weight / 2l
= 1.5 × 10-2 / 0.6
= 2.5 × 10-2 N/m
Therefore, the surface tension of the film is 2.5 × 10–2 N m–1

Answer 2

Hey mate,

◆ Answer-
T = 0.025 N/m

◆ Explanation-
# Given-
F = 1.5×10^-2 N
l = 30 cm = 0.3 m

# Solution-
Here, soap film will form on both sides of slider. i.e. l' = 2l

Surface tension of the soap film is given by-
Surface tension = Force / Length
T = F / 2l
T = 1.5×10^-2 / 2×0.3
T = 2.25×10^-2
T = 0.025 N/m^2

Surface tension of the soap film is 0.025 N/m^2.

Hope that is helpful...