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Question: A thin liquid film formed between a U shaped wire and a light slider supports a weight of \(1.5 \tim...

A thin liquid film formed between a U shaped wire and a light slider supports a weight of 1.5×10−2N,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

A

0.0125 N m−1\text{0.0125 N }\text{m}^{- 1}

B

0.1 N m−1\text{0.1 N }\text{m}^{- 1}

C

0.05 N m−1\text{0.05 N }\text{m}^{- 1}

D

0.025 N m−1\text{0.025 N }\text{m}^{- 1}

Answer

0.025 N m−1\text{0.025 N }\text{m}^{- 1}

Explanation

Solution

Here, W=1.5×10−2N,W = 1.5 \times 10^{- 2}N,

l=30cm=30×10−2ml = 30cm = 30 \times 10^{- 2}m

A liquid film has two free surfaces. A slider will support the weight when the force of surface tension acting upwards on the slider (=2Sl) balances the downwards force due to weight (= w)