Two spherical soap bubbles of radii a and b in vacuum coalesce under isothermal conditions. The resulting bubble has a radius given by

Step-by-step solution

Since, the bubbles coalesce in vacuum and there is no change in temperature, hence its surface energy does not change. This means that the surface area remains unchanged. Hence, 4 π a 2 + 4 π b 2 = 4 π R 2 or R = a 2 + b 2