The work done in increasing the size of a rectangular soap film with dimensions 8 cm x 3.75 cm to 10 cm x 6 cm is `2 xx 10^(-4) J`. The surface tension of the film in `(N m^(-1))` is

Options

A. `1.65 xx 10^(-2)`
B. `33 xx 10^(-2)`
C. `6.6 xx 10^(-2)`
D. `8.25 xx 10^(-2)`

Answer

B

Explanation

Since the soap film has two surfaces,
`:.` Increase in surface area, `Delta A = 2[10 xx 6-8 xx 3.75] xx 10^(-4) m^(2)`
Surface tension, `S = (W)/(Delta A)= (2 xx 10^(-4))/(2 xx [60 -30] xx 10^(-4)) = 3.3 xx 10^(-2) N//m`