Properties Of Solids And Liquids Question 359
Question: A film of water is formed between two straight parallel wires of length 10cm each separated by 0.5 cm. 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\times {{10}^{-2}}N/m) $ [MP PET 2001]
Options:
A)$ 7.22\times {{10}^{-6}}Joule $
B) $ 1.44\times {{10}^{-5}}Joule $
C) $ 2.88\times {{10}^{-5}}Joule $
D) $ 5.76\times {{10}^{-5}}Joule $
Show Answer
Answer:
Correct Answer: B
Solution:
Increment in area of soap film = $ A _{2}-A _{1} $
$ =2\times [(10\times 0.6)-(10\times 0.5)]\times {{10}^{-4}}=2\times {{10}^{-4}}m^{2} $
Work done = $ T\times \Delta A $
$ =7.2\times {{10}^{-2}}\times 2\times {{10}^{-4}}=1.44\times {{10}^{-5}}J $
