A film of water is formed between two straight parallel wires of length 10 cm each separated by `0.5cm` If their separation is increased by `1mm` while still maintaining their parallelism, how much work will have to be done (Surface tension of water `=7.2xx10^-2(N)/(m)`)

Options

A. `7.22 xx10^(-6)`J
B. `1.44 xx10^(-5)`J
C. `2.88 xx10^(-5)`J
D. `5.76 xx10^(-5)`J

Answer

B

Explanation

`S.T =("Work done")/("Increase in area") =(dW)/(dA)`
` :. dW = (TDA) xx 2 " "` (The factor two is used because the increase in area =2 (dA)
` = 2 xx 7.2 xx 10^(-2) xx 10xx10^(-2) xx 1xx 10^(-3)`
` = 1.44 xx10^(-5)` J