Which power quantity is zero for an ideal capacitor, indicating that it dissipates no real power?

Introduction:
This question probes understanding of power in reactive components. An ideal capacitor stores and releases energy without dissipating it as heat. Distinguishing between true, reactive, and apparent power clarifies why real power dissipation is zero in an ideal capacitor.

Given Data / Assumptions:

• Ideal capacitor with no equivalent series resistance (ESR).
• Sinusoidal steady state AC.
• Voltage and current are 90 degrees out of phase (current leads).

Concept / Approach:
Power types: true (real) power P, reactive power Q, and apparent power S. For a purely reactive element, average power over a cycle is zero because energy taken from the source during part of the cycle is returned during another part. Thus, true power equals zero. Reactive power is nonzero and measured in VAR, representing energy exchange with the field.

Step-by-Step Solution:

Verification / Alternative check:
Energy stored per cycle W = 0.5 * C * V^2 at peak and is returned each half cycle. No net energy accumulates as heat, confirming P = 0 W for the ideal case.

Why Other Options Are Wrong:

• Instantaneous power: Not always zero; it alternates in sign.
• Reactive power: Not zero; it quantifies energy exchange (VAR), not dissipation.
• Resistive power: Not a standard term; dissipation requires resistance, which an ideal capacitor lacks.

Common Pitfalls:
Confusing reactive and true power, assuming zero current, or ignoring ESR in practical capacitors, which introduces small but nonzero losses.

Final Answer:
True power is zero for an ideal capacitor, meaning it dissipates no real power.