Question

Please help?

A U shaped wire is dipped in soap solution and removed. The thin soap film formed between the wire and the light slider supports a weight of `1.5 xx 10^(-2) N` {including the weight of the slider}. The length of the slider is 30 cm. Find the surface tension of the soap solution?

Answer 1

Surface tension `gamma` of a liquid is the force per unit length.

The soap film formed on the U shaped wire has two sides, each of which contributes equally to the force.

Total weight supported by the soap film`=1.5xx10^-2\ N`
The length of the slider is `=30/100=0.3\ m`
Total force due to surface tension `=2xx"length"xxgamma=0.6gamma`

Equating the two we get

`0.6gamma=1.5xx10^-2`
`=>gamma=(1.5xx10^-2)/0.6=2.5xx10^-2\ Nm^-1`