Question

A soap bubble of radius r si blown up to form of bubble of radius 3r under isothermal conditions . What is the energy spent in doing so if the surface tension of soap solution is S.

Answer 1

A soap bubble has two free surface, so increase in surface area of soap bubble when radius changes from r to 3r is
`Delta A = 2 xx[4 pi (3r)^(2)- 4 pi r^(2)] = 64 pi r^(2)`
Energy spent= workdone = `S xx Delta A`
`= S xx 64 pi r^(2)`.