Physics Alternating Current ETEA 2009
PMDC Verified Question 123 of 127
The average power loss in a capacitor in an AC circuit is:
A
\(\langle P \rangle = V_0 I_0\)
B
\(\langle P \rangle = V_0 I_0 \sin\omega t\)
C
\(\langle P \rangle = V_0 I_0 \cos\omega t\)
D
\(\langle P \rangle = \text{Zero}\)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \(\langle P \rangle = \text{Zero}\)
Concept:

Because current leads voltage by \(90^\circ\) in a pure capacitor, the power factor \(\cos\phi = \cos(90^\circ) = 0\).

Formula / Reaction:

$$\langle P \rangle = V_{\text{rms}} I_{\text{rms}} \cos(90^\circ) = 0$$

Solution:

  • The capacitor acts as an energy storage element, storing energy electrostatically and releasing it back to the circuit without net thermal dissipation.


  • Thus, average power loss over a complete cycle is zero.


Why other options are incorrect:

  • Opt_A: Apparent peak power.


  • Opt_B, Opt_C: Time-dependent functions do not represent cycle-averaged power.

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