Q.

Surface tension of a soap bubble is 2.0×10-2 Nm-1. Work done to increase the radius of the soap bubble from 3.5 cm to 7 cm will be [Take π=227]          [2023]

1 0.72×10-4 J  
2 5.76×10-4 J  
3 18.48×10-4 J  
4 9.24×10-4 J  

Ans.

(3)

Surface area of soap bubble=2×4πR2

Work done=change in surface energy×Ts

           =Ts×8π×(R22-R12)

            =2×10-2×8×227×49×34×10-4

            =18.48×10-4 J