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Question: A film of water is formed between two straight parallel wires of length 10cm each separated by 0.5cm...

A film of water is formed between two straight parallel wires of length 10cm each separated by 0.5cm. If their separation is increased by 1 mm while still maintaining their parallelism, how much work will have to be done (Surface tension of water =7.2×10−2N/m= 7.2 \times 10^{- 2}N/m)

A

7.22×10−67.22 \times 10^{- 6}J

B

1.44×10−51.44 \times 10^{- 5} J

C

2.88×10−52.88 \times 10^{- 5} J

D

5.76×10−55.76 \times 10^{- 5} J

Answer

1.44×10−51.44 \times 10^{- 5} J

Explanation

Solution

As film have two free surfacesW=T×2ΔAW=T×2l×x\mathbf{W = T \times 2\Delta A}W = T \times 2l \times x

=7.2×10−2×2×0.1×1×10−3=1.44×10−5= 7.2 \times 10^{- 2} \times 2 \times 0.1 \times 1 \times 10^{- 3} = 1.44 \times 10^{- 5}J