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