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 x 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

Force on the slider,

F = 1.5 x 10^-2 N

Length, (l) = 30 cm = 30/100 m = 0.3 m

Surface tension, T = F/2l = {1.5 x 10^-2}/{2 x 0.3} = 2.5 x 10^-2 Nm^-1

A factor of 2 is taken (for S = F/2l) because there are two sides of slider acted upon by the force F.