Energy storage mechanism – Which field stores energy in a capacitor? Statement: “Energy is stored by a capacitor in a magnetic field.” Choose the correct evaluation.
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AFalse
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BTrue
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CTrue only at high frequency
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DTrue for nonpolar dielectrics only
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ETrue if current is large enough
Answer
Correct Answer: False
Explanation
Introduction / Context:Understanding where energy resides in reactive components is central for safe design, energy density estimation, and transient behavior. Capacitors and inductors store energy in different physical fields.
Given Data / Assumptions:
- Ideal lumped components: capacitor (C) and inductor (L).
- No parasitic coupling or significant losses.
- Standard field relationships apply.
Concept / Approach:
A capacitor stores energy in its electric field between plates: Wc = (1/2) * C * V^2. An inductor stores energy in its magnetic field: WL = (1/2) * L * I^2. Therefore, the statement that a capacitor stores energy in a magnetic field is false; that description belongs to an inductor.
Step-by-Step Solution:
For a charged capacitor, electric field E exists between plates; energy density ue = (1/2) * ε * E^2.Total stored energy integrates ue over the volume → Wc = (1/2) * C * V^2.Magnetic energy corresponds to inductors where energy density um = (1/2) * B * H and WL = (1/2) * L * I^2.Thus, the given statement is incorrect.Verification / Alternative check:
Discharge a capacitor across a resistor: energy released equals (1/2) * C * V^2, consistent with purely electric-field storage; no magnetic core is required for a capacitor to store energy.
Why Other Options Are Wrong:
Frequency, dielectric type, or current magnitude do not convert a capacitor’s storage mechanism from electric to magnetic field. Any magnetic effects near currents are incidental and small for ideal capacitor operation.
Common Pitfalls:
Associating the presence of current during charging with magnetic energy storage; mixing up inductor and capacitor roles in LC resonant tanks.
Final Answer:
False.