Physics Alternating Current ETEA 2010
PMDC Verified Question 121 of 127
The capacitive reactance of the AC circuit increases:
A
By increasing the frequency of AC
B
By decreasing the frequency of AC
C
Does not depend upon the frequency of AC voltage
D
None of these
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: By decreasing the frequency of AC
Concept:

Capacitive reactance \(X_C\) is the opposition offered by a capacitor to the flow of alternating current and is inversely proportional to frequency.

Formula / Reaction:

$$X_C = \frac{1}{\omega C} = \frac{1}{2\pi f C}$$

Solution:

  • Because \(X_C \propto \frac{1}{f}\), decreasing the frequency \(f\) of the AC source causes the capacitive reactance \(X_C\) to increase.


  • In the limit of direct current (\(f = 0\)), \(X_C \to \infty\), completely blocking steady DC.


Why other options are incorrect:

  • Opt_A: Increasing the frequency decreases \(X_C\).


  • Opt_C: Reactance is explicitly frequency-dependent.


  • Opt_D: Option B is correct.

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