A rectangular film of liquid is extended from `(4cmxx2cm)` to `(5cmxx4cm)`. If the work done is `3xx10^-4J`, 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

`W=2(T DeltaA)`
`DeltaA=A_(2)-A_(1)`
`=(20-8)xx10^(-4)m^(2)`
`=12xx10^(-4)m^(2)`
`T=(W)/(2DeltaA)=(3xx10^(-4))/(2xx12xx10^(-4))`
`T=(1)/(8)Nm=0.125N//m`