Question

Find the amount of work done in forming a soap film of size $5\text{cm}\times 15\text{cm}$, if surface tension is ${10}^{-2}\text{N/m}$.

• A. $3\times {10}^{-4}\text{J}$
• B. $1.5\times {10}^{-4}\text{J}$
• C. $2\times {10}^{-4}\text{J}$
• D. $2.5\times {10}^{-4}\text{J}$

Answer 1

The correct option is B $1.5\times {10}^{-4}\text{J}$

As we know,
Soap film has two layer.
$\therefore$Total surface area of soap film$=2\times (5\text{cm}\times 15\text{cm})$
$=150\times {10}^{-4}{\text{m}}^2$
Initial surface area of soap film is $0{\text{m}}^2$

Work done in forming soap film,$W=T\Delta A$
$={10}^{-2}\times (150\times {10}^{-4}-0)\text{J}$
$=1.5\times {10}^{-4}\text{J}$