Q. A water film is formed between two parallel wires of 10 cm length. The distance of 0.5 cm between the wires is increased by 1 mm. Which will be the work done? (Surface tension of water =$72\ {Nm}^{- 1})$
A) 288 erg
B) 144 erg
C) 72 erg
D) 36 erg
Explanation
(b) $W = 2 \times T \times \mathrm{\Delta}A$
$= 2 \times 72 \times (0.6 - 0.5) \times 10 = 144\ erg$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.