Final answer:
Inserting a dielectric material into a disconnected parallel plate capacitor increases its capacitance, reduces the potential difference across the plates without changing the charge, and alters the energy stored in the capacitor.
Step-by-step explanation:
When a dielectric material with a given dielectric constant is inserted into a parallel plate capacitor, the capacitance of the capacitor increases. This increase in capacitance happens because the dielectric reduces the electric field within the capacitor, which allows more charge to be stored for a given potential difference when the capacitor is connected to a battery. When the capacitor is disconnected from the power supply before the insertion of the dielectric, the charge on the plates remains constant, but the potential difference across the plates decreases because the capacitance increases. The energy stored in the capacitor also changes due to the insertion of the dielectric material.
If we consider a specific example, such as the insertion of a paper with a dielectric constant of 3.7 between the plates, the capacitance would become 3.7 times greater than when the space was filled with air (assuming the dielectric completely fills the space between the plates and there is no leakage of charge). Consequently, the potential difference across the plates would decrease to 1/3.7 of its original value when the battery was first disconnected, while the charge remains the same. The energy stored in the capacitor also increases because energy is proportional to both the capacitance and the square of the potential difference. This concept is crucial in designing circuits that require certain capacitance and voltage characteristics.