Q. A frame made of a 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
$E = S \times 2A$
New surface energy, $E_{1} = S \times 2(A/2) = S \times A$
% decrease in surface energy $= \frac{E - E_{1}}{E} \times 100$
$= \frac{2\ SA - SA}{2\ SA} \times 100 = 50\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.