1. The problem statement, all variables and given/known data Find the amount of charge required to double the radius of a bubble of radius r and surface tension T. 2. Relevant equations Increase in surface energy of bubble = T ΔA 3. The attempt at a solution I've tried equating the increase in surface energy to the work done by the Coulomb force, but I'm finding a lack of information. Do I just assume that the charge is some distance away from the bubble? Then what will be the integration limits for F . dr?