First slide

Surface tension

Question

A thin liquid film formed between a U shaped wire and a light slider supports a weight of $1.5 \times 10^{- 2}$ N, as shown in the figure. The length of the slider is 30 cm and its weight negligible. The surface tension of the liquid film is

Moderate

A

0.0125 N $m^{- 1}$
B

0.1 N $m^{- 1}$
C

0.05 N $m^{- 1}$
D

0.025 N $m^{- 1}$

Solution

Here,W = $1.5 \times 10^{- 2} N,$
l = 30 cm = 30 x $10^{- 2}$ m
A liquid film has two free surfaces. A slider will support the weight when the force of surface tension action upwards on the slider (2SI) balances the downward force due to weight (=W)

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