1. The problem statement, all variables and given/known data The metallic sphere on top of a large van de Graaf generator has a radius of 2.0 m. Suppose that the sphere carries a charge of 3x10-5 C. How much energy is stored in this device? 2. Relevant equations So the equation I must use is this: U = 1/2C(ΔV)^2 Q is given; 3 x 10 ^ -5C To find ΔV, I'd first the formula :V = Q/(4∏ε0r) 3. The attempt at a solution Then it's simply a matter of plugging the numbers. The formula I'm not sure is how to find ΔV from the information, I'm not sure I'd be using the right one.