A parallel-plate vacuum capacitor has 6.88 J of energy stored in it. The separation between the plates is 2.00 mm. If the separation is decreased to 1.70 mm, what is the energy now stored if the capacitor was disconnected from the potential source before the separation of the plates was changed? U = ___ J

A parallel-plate vacuum capacitor has 6.88 J of energy stored in it. The separation between the plates is 2.00 mm. If the separation is decreased to 1.70 mm, what is the energy now stored if the capacitor was disconnected from the potential source before the separation of the plates was changed? U = ___ J