Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 29 of 127
When a steady DC source (\(f = 0\text{ Hz}\)) is connected across an ideal capacitor, the steady-state capacitive reactance is:
A
Zero
B
\(1\ \Omega\)
C
Finite and constant
D
Infinite
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Infinite
Concept:

Direct current maintains a constant unidirectional potential, corresponding to zero frequency (\(f = 0\)).

Formula / Reaction:

$$X_C = \lim_{f \to 0} \frac{1}{2\pi f C} = \infty$$

Solution:

  • Because \(f = 0\) for a steady DC source, the denominator \(2\pi f C = 0\).


  • Therefore, \(X_C \to \infty\), meaning an ideal capacitor acts as an open circuit to steady DC after charging.


Why other options are incorrect:

  • Opt_A: Reactance approaches zero at infinite frequency (\(f \to \infty\)), not at DC.


  • Opt_B: \(1\ \Omega\) is an arbitrary finite value.


  • Opt_C: Reactance is infinite, completely blocking steady current.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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