Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 73 of 127
A pure capacitor is connected across an AC voltage source of constant amplitude and frequency. If a dielectric slab of dielectric constant \(\kappa > 1\) is inserted between the capacitor plates, the alternating current in the circuit will:
A
Decrease
B
Increase
C
Remain unchanged
D
Drop to zero
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Increase
Concept:

Inserting a dielectric increases capacitance (\(C' = \kappa C\)), which decreases capacitive reactance and increases circuit current.

Formula / Reaction:

$$C' = \kappa C, \quad X_C' = \frac{1}{2\pi f C'} = \frac{X_C}{\kappa}, \quad I_{\text{rms}} = \frac{V_{\text{rms}}}{X_C'} = \kappa I_{\text{rms}}$$

Solution:

  • Because \(\kappa > 1\), capacitance increases.


  • Capacitive reactance decreases, allowing a larger alternating current to flow.


Why other options are incorrect:

  • Opt_A: Current would decrease only if reactance increased.


  • Opt_C: Reactance changes when dielectric constant changes.


  • Opt_D: Current increases, not drops to zero.

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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