Question

A thin liquid film formed between a U-Shaped wire and a light slider supports a weight of 1.5 x 10^-2 (see figure) The length of the slider is 30 cm and it's weight is negligible. The surface tension of the liquid film is?

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Answer 1

A think film formed between a U - shaped wire and a light slider supports a weight of 1.5 × 10¯² N. The length of the slider is 30 cm and its weight is negligible.

To find : The surface tension of the liquid film is ...

solution : at equilibrium,

The force due to surface tension is balanced by weight.

i.e., F = W

here W = 1.5 × 10¯² N

l = 30 cm = 30 × 10¯² m

a liquid has two film surfaces. so, F = 2Tl

now, 2Tl = W

⇒2 × T × 30 × 10¯² = 1.5 × 10¯²

⇒T = 1.5/60 = 1/40 = 0.025 N/m

Therefore the surface tension of the liquid will be 0.025 N/m