A 4.00-F air gap capacitor is connected to a 100.0-V battery until the capacitor is fully charged.

Question:

A 4.00-μF air gap capacitor is connected to a 100.0-V battery until the capacitor is fully charged. The battery is removed and then a dielectric of dielectric constant 6.0 is inserted between the plates without allowing any charge to leak off the plates.
(a) Find the energy stored in the capacitor before and after the dielectric is inserted.
(b) Does an external agent have to do positive work to insert the dielectric or to remove the dielectric? Explain.