A battery charges a parallel-plate capacitor fully and then is removed. The plates are immediately pulled apart. (With the battery disconnected, the amount of charge on the plates remains constant.What happens to the potential difference between the plates as they are being separated?"

Three reasons for adding a dielectric material between the plates of a capacitor.
1. Dielectrics do not break down (allowing electric charge to flow"as readily as air, so a higher voltage can be applied without charge passing across the gap.
2. A dielectric allows the plates to be placed closer together without touching thus allowing an increased capacitance because the plate separation is less.
3. If a dielectric fills the space between the two conductors, it increases the capacitance.