A2L Item 217

Goal: Reason regarding capacitors and dielectrics.

Source: 283-535 inserting a dielectric changes a capacitor

A capacitor with capacitance C is connected to a battery until charged,
then disconnected from the battery. A dielectric having constant
κ is inserted in the capacitor. What changes occur in the charge,
potential and stored energy of the capacitor after the dielectric is

  1. V stays same, Q increases, U increases
  2. V stays same, Q decreases, U stays same
  3. V increases, Q decreases, U increases
  4. V decreases, Q stays same, U decreases
  5. None of the above
  6. Cannot be determined



(4) It should be clear to students that the charge cannot change. Most
students recognize that capacitance increases when a dielectric is
inserted into a capacitor. The issue then becomes whether they
appreciate the relationships between C, Q, V and U.