A parallel-plate capacitor is initially charged to a potential difference of by an…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A parallel-plate capacitor is initially charged to a potential difference of V0 by an ideal battery and then disconnected so that the charge on the plates remains constant. A dielectric slab with constant κ that completely fills the space between the plates is then slowly inserted until it occupies the full region between the plates. Frictional and edge effects are negligible.
(a) Describe qualitatively how the capacitance, the electric‐field magnitude between the plates, and the potential difference across the plates change as the slab is inserted.
(b) Explain whether the energy stored in the capacitor increases, decreases, or remains unchanged. Support your answer with appropriate reasoning based on the quantities identified in part (a).
(c) The same dielectric slab is now inserted while the capacitor remains connected to the ideal battery (so the potential difference is held at V0). Describe and explain how the capacitance, charge on the plates, and stored energy compare with their original values in this case.