An air-gap parallel-plate capacitor of capacitance is charged to and then…
PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Electric fields in matter · Electric fields in matter
Electricity, Magnetism and Electromagnetism, Ch Dielectrics: polarisation, bound charge and the displacement field
Problem
An air-gap parallel-plate capacitor of capacitance C0=220pF is charged to 150V and then disconnected from the supply, so its charge cannot change and the air gap is treated as vacuum. A snugly fitting slab of a linear dielectric with εr=6.0, carrying no free charge, is then slid in until it fills the gap completely. Edge effects and any friction are ignored.
((a)) Predict, with a reason, whether the stored energy rises or falls.
((b)) Find the stored energy before and after the slab is fully in.
((c)) Find the potential difference across the capacitor after insertion.
((d)) Find the energy transferred out of the field, and say what it went into.