Manipal Entrance Test 2013 Physics Paper

The surface tension (T) of a liquid is equal to the work (W) required to increase the surface area of the liquid film by unity at constant temperature.
As per key idea, tension
=

work‌done

surface‌area

or T=

W

ΔA

Since soap bubble has two surface and surface area of soap bubble is 4πR2
where R is radius of bubble.
then W=T×2×4πR2
Given R=2R
therefore W=T×2×4π×(2R)2
W=32πR2T