If the surface tension of a soap is 3 × 10⁻² N/m then the work done in forming a soap film of 20 cm × 5 cm will be (a) 6 × 10⁻² J (b) 6 J (c) 6 × 10⁻⁴ J (d) 6 × 10⁻³ J

Answer: (c). A soap film has two surfaces, so W = T × 2A. A = 20 cm × 5 cm = 100 cm² = 10⁻² m² W = 3×10⁻² × 2 × 10⁻² = 6×10⁻⁴ J So the answer is (c) 6×10⁻⁴ J.

If the surface tension of a soap is 3 × 10⁻² N/m then the work done… | MHT CET 2020 (19 Oct, Shift 2)

Q27MHT CET 2020 · 19 OCT · SHIFT 2Easy

Surface Energy & Work Done

If the surface tension of a soap is $3 \times 10^{-2}\text{ N/m}$ then the work done in forming a soap film of $20\text{ cm} \times 5\text{ cm}$ will be

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Answer: (c)

A soap film has two surfaces, so $W = T \times 2A$ .
$A = 20\text{ cm} \times 5\text{ cm} = 100\text{ cm}^2 = 10^{-2}\text{ m}^2$
$W = 3\times10^{-2} \times 2 \times 10^{-2} = 6\times10^{-4}\text{ J}$
So the answer is (c) $6\times10^{-4}\text{ J}$ .

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Surface Energy & Work Done question from MHT CET 2020 (19 Oct, Shift 2)

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