If radius (r) of a circle made two times (2r) then change in area =π(2r)2−πr2 =3πr2=3×‌ initial area ‌ Here, initial area of soap film, A1=10cm2 Final area has a radius twice that of initial radius. So, change in area △A=3A1=3×10cm2 =3×10×10−4m2 =3×10−3m2 As, a liquid film has two surfaces (one top and other bottom). Change in surface energy or work done, W=2△A×T T= Surface tension or T=W∕2△A Here, W=8×10−3J ∆A=30×10−3m2 So, surface tension of Liquid, T=