Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 55 of 127
If the frequency of an AC voltage source across a pure capacitor is decreased to one-fourth (\(1/4\)) of its original value, its capacitive reactance will:
A
Decrease to one-fourth
B
Double
C
Quadruple (increase by 4 times)
D
Remain constant
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Quadruple (increase by 4 times)
Concept:

Capacitive reactance is inversely proportional to frequency: \(X_C \propto \frac{1}{f}\).

Formula / Reaction:

$$X_C' = \frac{1}{2\pi (f/4) C} = 4 \left( \frac{1}{2\pi f C} \right) = 4X_C$$

Solution:

  • Reducing frequency by a factor of 4 increases the opposition \(X_C\) by a factor of 4.


Why other options are incorrect:

  • Opt_A: Direct proportionality error (confusing with \(X_L\)).


  • Opt_B: Incorrect scaling.


  • Opt_D: Reactance is strictly frequency-dependent.

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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