A parallel-plate vacuum capacitor has 8.28 J of energy stored in it. The separation between the plates is 2.30 mm. If the separation is decreased to 1.00mm. What is the energy now stored if the capacitor was disconnected from the potential source before the separation of the plates was changed? I really don't know what to do I know that U=Q^2 / 2C = .5*C*V^2 = .5*Q*V I read through the entire chapter but I don't see anything about how the potential energy changes when the capacitor is disconnected from the potential source can anyone help?