Q. A frame made of metallic wire enclosing a surface area $A$ is covered with a soap film. If the area of the frame of metallic wire is reduced by 50% , the energy of the soap film will be changed by
A) 100%
B) 75%
C) 50%
D) 25%
Explanation
(c) $Surface\ energy = surface\ tension \times surface\ area\ $
$E = T \times 2A$
New surface energy,
$E_{1} = T \times 2\left( \frac{A}{2} \right) = T \times A$
$\%\ decrease\ in\ surface\ energy = \frac{E - E_{1}}{E} \times 100$
$\ = \frac{2TA - TA}{2TA} \times 100 = 50\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.