Question

The work done in increasing the size of a rectangular soap film with dimensions 8cm x 3.75cm to 10 cm x 6 cm is 2 x 10${}^{-4}$ J.The surface tension of the film in N/m is:

• A. 165 x 10${}^{-2}$
• B. 3.3 x 10${}^{-2}$
• C. 6.6 x 10${}^{-2}$
• D. 8.25 x 10${}^{-2}$

Answer 1

Answer: (B)

3.3 x 10${}^{-2}$

$\Delta A=2[10\times 6-8\times 3.75]$
$=60c{m}^2$

$\Delta \bigcup =2\times {10}^{-4}J$
$2\times {10}^{-4}=60\times {10}^{-4}\times T$
$3.3\times {10}^{-2}N/m=T$