Question

Consider a soap film on a rectangular frame of wire of area $4\times 4c{m}^2$. If the area of the soap film is increased to $4\times 5c{m}^2$, the work done in the process will be
(The surface tension of the soap film is $3\times 10^{-2}N/m.$ )

• A. $12\times 10^{-6}J$
• B. $24\times 10^{-6}J$
• C. $60\times 10^{-6}J$
• D. $96\times 10^{-6}J$

Answer 1

Answer: (B)

Work done, $W=2T\times A$
$W=6\times 10^{-2}\times [4\times 5-4\times 4]\times 10^{-4}$
$=6\times 10^{-6}\times 4$
$=24\times 10^{-6}J$
(Film has two free surfaces).