A parallel plate capacitor (with air between plates) is connected to a battery until it is fully charged. At this point there is certain charge on the plates and a certain potential difference between the plates. With the battery still connected, a dielectric material is forced between the plates. Which of the following quantities is unchanged?
  1. the electric displacement D
  2. the electric field E
  3. the potential difference ΔV
  4. the charge on the plates Q
  5. (a),(d)
  6. (b),(c)
  7. none of the above