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 xx 10 ^(-6)` joule
B. `1.44 xx 10 ^(-5)` joule
C. `2.88 xx 10 ^(-5)` joule
D. `5.76 xx 10 ^(-5)` joule

Answer

B

Explanation

Increment in area of soap film `= A _(2) -A_(1)`
`=2 xx [ (10 xx 0.6) - (10 xx 0.5) ] xx 10 ^(-4) =2 xx 10 ^(-4) m ^(2)`
Work done `= R xx Delta A = 7. 2 xx 10 ^(-2) xx 2 xx 10 ^(-4) = 1. 44 xx 10 ^(-5)J`