Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 32 of 127
When an alternating current flows through a pure inductor, the phase relationship between the alternating voltage \(V\) and alternating current \(I\) is:
A
Current leads voltage by \(90^\circ\)
B
Voltage leads current by \(90^\circ\)
C
Voltage and current are in phase
D
Voltage leads current by \(180^\circ\)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Voltage leads current by \(90^\circ\)
Concept:

In an inductor, self-induced emf opposes the rate of growth of current, causing current changes to lag behind applied voltage changes by a quarter cycle.

Formula / Reaction:

$$v(t) = V_0 \sin(\omega t) \implies i(t) = I_0 \sin\left(\omega t - \frac{\pi}{2}\right)$$

Solution:

  • The voltage across an inductor peaks when current is zero and changing at its fastest rate.


  • Therefore, voltage leads current by \(90^\circ\) (or current lags voltage by \(90^\circ\)).


Why other options are incorrect:

  • Opt_A: Current leads voltage by \(90^\circ\) in a pure capacitor.


  • Opt_C: In-phase relationship occurs in a pure resistor.


  • Opt_D: A \(180^\circ\) phase difference represents complete opposition, not a pure inductive response.

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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