Q. A water film is made between two straight parallel wires of length 10 cm separated by 5 mm from each other. If the distance between the wires is increased by 2 mm. How much work will be done? Surface tension for water is $72\ dyne\ cm^{- 1}$
A) 288 erg
B) 72 erg
C) 144 erg
D) 216 erg
Explanation
(a) Work done = surface tension $\times$ increase in area
$= 72 \times \lbrack 10 \times 0.7 - 10 \times 0.5\rbrack \times 2$
$= 288$ erg
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.