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

Options

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

Answer

d

Explanation

Film has two free surfaces ,
`thereforeDeltaA=2[(5xx4)xx10^(-4)-(4xx2)xx10^(-4))]`
`=2[20xx10^(-4)-8xx10^(-4)]`
`=2xxx12xx10^(-4)`
`=24xx10^(-4)m^(2)`
`therefore` Work `W=2TDeltaA`
`3xx10^(-4)=24xx10^(4)xxT`
`thereforeT=(3xx10^(-4))/(24xx10^(-4))`
`thereforeT=(1)/(8)`
`thereforeT=0.125Nm^(-1)`