Energy storage principle: Does a capacitor store electric energy primarily in the electric field established between its plates?

Difficulty: Easy

Correct Answer: Correct

Explanation:


Introduction / Context:
Understanding where and how energy is stored in passive components is fundamental to circuit design. Capacitors and inductors are complementary: capacitors store energy in electric fields, while inductors store energy in magnetic fields. Recognizing this helps explain transient behavior, resonance, and filter dynamics.


Given Data / Assumptions:

  • Ideal parallel-plate capacitor viewpoint.
  • Uniform field approximation within the dielectric.
  • Negligible leakage and series resistance for energy accounting.


Concept / Approach:
The energy stored in a capacitor is E = 0.5 * C * v^2. This energy physically resides in the electric field in the dielectric volume between the plates. Increasing voltage strengthens the field (E-field magnitude), increasing stored energy. Geometry and dielectric constant determine C, hence energy density for a given voltage.


Step-by-Step Solution:

Charge the plates to voltage v; equal/opposite charges reside on facing surfaces.An electric field forms across the dielectric, with energy density proportional to epsilon * E^2 / 2.Total energy integrates to 0.5 * C * v^2 across the field volume.Removing the source leaves the energy stored until discharged through a load or loss.


Verification / Alternative check:
Transient RC behavior releases the stored energy into the resistor as heat when discharging, consistent with energy conservation. Field simulations show energy concentrated within the dielectric region.


Why Other Options Are Wrong:

Incorrect: contradicts basic electromagnetics.Only DC / only with inductors / only at resonance: capacitor field energy exists whenever a voltage is present, regardless of AC or DC, and does not require inductors or resonance.


Common Pitfalls:
Assuming energy is stored on the plates rather than in the field; conflating charge quantity with stored energy magnitude.


Final Answer:
Correct

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