A dielectric slab is inserted between the plates of an isolated charged capacitor. Which of the following quantities remain unchanged?

Concept:

Effect of Inserting a Dielectric Slab:

• When a dielectric slab is inserted between the plates of a charged capacitor, the following effects are observed:
  • The capacitance increases due to the dielectric constant of the material.
  • If the capacitor is isolated (not connected to a battery), the charge on the plates remains constant, as no external source is available to change the charge.
  • The potential difference between the plates decreases, as the dielectric reduces the effective electric field between the plates.
  • The stored energy in the capacitor decreases because energy is proportional to the square of the voltage, and the voltage decreases.
  • The electric field inside the capacitor also decreases, since the dielectric reduces the field between the plates.

Explanation:

Since the capacitor is isolated, the charge remains constant. The insertion of the dielectric only affects the electric field, voltage, and energy stored in the capacitor. The charge on the capacitor does not change because there is no external circuit to either supply or remove charge.

∴ The charge on the capacitor remains unchanged, which corresponds to Option 1.