A soap bubble of radius r is blown up to form a bubble of radius 3 r under isothermal conditions. If is the surface tension of soap solution, then the energy spent in blowing is

Step-by-step solution

Surface area of bubble of radius, r=4 r² Surface area of bubble of radius, 3 r=4 (3 r)²=36 r² Therefore, increase in surface area =36 r²-4 r²=32 r² Since, a bubble has two surfaces, the total increase in surface area =2 32 r²=64 r² Energy spent = Work done = Surface tension Total increase in surface area =64 r²