A rectangular film of liquid is extended from `(4 cm xx 2 cm)` to `(5 cm xx 4 xx cm)`. If the work done is `3 xx 10^(-4)J`, the value of the surface tension of the liquid is

Options

A. `0.250 Nm^(-1)`
B. `0.125 Nm^(-1)`
C. `0.2 Nm^(-1)`
D. `8.0 Nm^(-1)`

Answer

B

Explanation

Increase in surface area,
`DeltaA=(5 xx 4-4xx2) xx 2` `(therefore` film has two surface)
`=(20-8) xx 2 cm^(2)= 24 xx 10^(-4) m^(2)`
So, work done, W`=TDeltaA`
`3 xx 10^(-4) = T xx 24 xx 10^(-4)`
`therefore T=1/8=0.125 Nm^(-1)`