Question

The work done in increasing the size of a rectangular soap film with dimensions $8cm\times 3.75cm$ to $10cm\times 6cm$ is $2\times 106\times {10}^{-4}J$. The surface tension of the film in ($N{m}^{-1}$) is

• A. $1.65\times {10}^{-2}$
• B. $3.3\times {10}^{-2}$
• C. $6.6\times {10}^{-2}$
• D. $8.25\times {10}^{-2}$

Answer 1

The correct option is B $3.3\times {10}^{-2}$

we know that,

Surface Energy $=2\left(SurfaceTension\right)\times Area$

Work done $=$ change in surface energy $=2T\left(\Delta A\right)$

$T=\frac{W.D}{2\left(\Delta A\right)}=\frac{\Delta SE}{2\left(\Delta A\right)}$

$\Rightarrow T=\frac{2\times 106\times {10}^{-6}J}{2(60\times {10}^{-4}-8\times 3.75\times {10}^{-4}{m}^2)}$

$T=3.5\times {10}^{-2}N/m$

Option $B$ is correct.