Question

How much work must be done in blowing a spherical soap bubble 20 cm in diameter? The area of a sphere is 4πr² and the surface tension of the soap solution is 0.032 N/m.

Answer 1

The work is

$$W=\sigma\Delta A=\sigma(A_2-A_1),\\ W=4\pi\sigma(R^2-r^2)=\\ =4\cdot3.14\cdot0.032(0.1^2-0)=4.02\cdot10^{-3}\text{ J}.$$