A film of water is formed between two straight parallel wires each `10 cm` long and at a seperation of `0.5 cm`. Calculate the work required to increase `1mm` distance between the wires. Surface tension of water `=72xx10^(-3)N//m`.

Options

A. `1.44xx10^(-5)J`
B. `1.72xx10^(-5)J`
C. `1.44xx10^(-4)J`
D. `1.72xx10^(-4)J`

Answer

A

Explanation

As we increase the separation between the wire by `1mm`, the increase in surface area of the film is
`/_\A=2xx0.1xx10^(-3)=2xx10^(-4)m^(2)`
(as there are two surfaces of film)
So, increase in suface energy `/_\U=S/_\A=1.44xx10^(-5)J`
Work done`=/_\J`