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 file?
Surface tension, S is written as
S= 
Where,
‘F’ is the Force exerted or weight supported between the wire and the slider
‘l’ is the length of the slider.
Given,
The force exerted, F =1.5 × 10-2 N
The length of the slider, l =30 cm = 0.30 m
The soap film has two free surfaces thus,
Total length = 2l = 2 × 0.30 m = 0.6 m
Therefore, the surface tension, S =
⇒ S = 2.5 × 10-2 N / m
The surface tension of the file is 2.5 × 10-2 N /m
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