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 N m^(-1)`

Answer

B

Explanation

Work done= Surface tension of film `xx` change in area of the film or `W= T xx Delta A`
Here, `A_(1) = 4cm xx 2cm = 8cm^(2)`
`A_(2) = 5cm xx 4cm = 20cm^(2)`
Delta A= 2(A_(2) - A_(1)) = 24 cm^(2) = 24 xx 10^(-4) m^(2)`
`W= 3 xx 10^(-4) J, T=` ?
`:. T= (W)/(Delta A) = (3 xx 10^(-4))/(24 xx 10^(-4)) = (1)/(8) = 0.125 Nm^(-1)`