The behavior of a parallel-plate capacitor can change dramatically when a dielectric…
PHYSICS · Multi-part · CBSE · Physics · Electrostatic Potential and Capacitance · Electrostatic Potential and Capacitance
Problem
The behavior of a parallel-plate capacitor can change dramatically when a dielectric is inserted between its plates. Consider two identical capacitors, each initially consisting of two fixed plates of area A separated by a distance d with air filling the gap. In both cases the capacitors are first charged to the same initial potential difference ΔV0.
• In Case 1, the capacitor remains connected to the charging battery while a dielectric slab of constant κ that exactly fills the gap is slowly inserted.
• In Case 2, the capacitor is disconnected from the battery so the charge remains fixed, and then the same dielectric slab is inserted.
(a) For Case 1, qualitatively describe how each of the following quantities changes, if at all, as the dielectric is inserted: capacitance, charge on each plate, potential difference, electric field magnitude between the plates, and energy stored.
(b) Repeat part (a) for Case 2.
(c) Using energy considerations, explain why external work must be done in one case but the capacitor does work on its surroundings in the other case.
(d) Identify one practical application that exploits the change in capacitance produced by inserting or removing a dielectric, and briefly explain how the device makes use of this effect.