Question

If T is the surface tension of soap solution, the amount of work done in blowing a soap bubble from a diameter D to 2D is

• A. 2$\pi D ^ { 2 } T$
• B. 4$\pi D ^ { 2 } T$
• C. 6$\pi D ^ { 2 } T$
• D. 8$\pi D ^ { 2 } T$

Answer 1

Answer: (C)

6$\pi D ^ { 2 } T$

Answer 2

Work done to increase the diameter of bubble from d to D

$W = 2 \pi \left( D ^ { 2 } - d ^ { 2 } \right) T = 2 \pi \left[ ( 2 D ) ^ { 2 } - ( D ) ^ { 2 } \right] T = 6 \pi D ^ { 2 } T$