Calculate the work done against surface tension in blowing a soap bubble from a radius of 10cm to 20 cm if the surface tension of soap solution is $25\times {10}^{-3}\mathrm{N}/\mathrm{m}$. $\left(\_\_\_\_\_\_\mathrm{\pi }\times {10}^{-3}\mathrm{J}\right)$

 $\mathrm{Inital}\mathrm{total}\mathrm{surface}\mathrm{area}=2\times 4{{\mathrm{\pi r}}_1}^2=2\times 4\mathrm{\pi }\times {(0.1)}^2$
$\mathrm{Find}\mathrm{total}\mathrm{surface}\mathrm{area}=2\times 4{{\mathrm{\pi r}}^2}_2=2\times 4\mathrm{\pi }\times {(0.2)}^2$
$\mathrm{extension}\mathrm{in}\mathrm{area}=2\times 4\mathrm{\pi }[{(0.2)}^2-{(0.1)}^2]=0.24\mathrm{\pi }$
$\begin{array}{l}\mathrm{workdone}\mathrm{w}=\mathrm{T}\times △\mathrm{A}\\ =25\times {10}^{-3}\times 0.24\mathrm{\pi }=6\mathrm{\pi }\times {10}^{-3}\mathrm{J}\end{array}$