Question

Consider a soap film on a rectangular frame of wire of area $4 \times 4\, cm ^{2}$. If the area of the soap film is increased to $4 \times 5 \,cm ^{2}$, 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, $W=2 T \times A$
$W=6 \times 10^{-2} \times[4 \times 5-4 \times 4] \times 10^{-4}$
$=6 \times 10^{-6} \times 4$
$=24 \times 10^{-6} J$
(Film has two free surfaces).