1. The problem statement, all variables and given/known data A sphere of radius R has a charge Q distributed uniformly over its surface. How large a sphere contains 90 percent of the energy stored in the electrostatic ﬁeld of this charge distribution? 2. Relevant equations U= 1/8pi integral E^2dv. 3. The attempt at a solution I was able to derive that the energy to assemble a shell is Q^2/2R. The problem is idk what kind of sphere they are talking about? Do they mean a hollow sphere or one with a charge density?