Q. A rectangular film of liquid is extended from (4 cm × 2 cm) to (5 cm × 4 cm). If the work done is $3 \times 10^{-4}$ J, the value of the surface tension of the liquid is
A) 0.250 $Nm^{-1}$
B) 0.125 $Nm^{-1}$
C) 0.2 $Nm^{-1}$
D) 8.0 $Nm^{-1}$
Explanation
[Solution] A film has two surfaces: $\Delta A = 2(20 - 8) = 24$ $cm^2$ $= 24 \times 10^{-4}$ $m^2$; $T = W/\Delta A = 0.125$ N/m. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.