Q: If the surface tension of soap solution is 35 dynes/cm, calculate the work done to form an air bubble of diameter 14 mm with that solution.
Sol: Surface tension T = 35 dynes/cm = 0.035 N/m
Radius of the bubble r = 14 mm/2 = 7 mm = 7× 10-3 m
W = ΔA × T = 8 π r2 T = 8 × 22/7 × 49 × 10-6 × 0.035
W = 4.312 × 10-5 J