Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 1 of 127
An alternating voltage source is connected to a resistor \( R \) and a capacitor \( C \) in series. Which of the following statements about the phase angle between voltage \( V \) and current \( I \) is correct?
A
In the resistor, \( I \) leads \( V \) by \( 90^\circ \) - In the capacitor, \( I \) leads \( V \) by \( 90^\circ \)
B
In the resistor, \( I \) and \( V \) are in phase - In the capacitor, \( I \) lags \( V \) by \( 90^\circ \)
C
In the resistor, \( I \) and \( V \) are in phase - In the capacitor, \( I \) leads \( V \) by \( 90^\circ \)
D
In the resistor, \( I \) lags \( V \) by \( 90^\circ \) - In the capacitor, \( I \) leads \( V \) by \( 90^\circ \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: In the resistor, \( I \) and \( V \) are in phase - In the capacitor, \( I \) leads \( V \) by \( 90^\circ \)
Concept:

Phase difference defines the timing relationship between current and voltage waves in different circuit elements.

Solution:

  • In a purely resistive element, the voltage and current are always in phase (phase angle \( \theta = 0^\circ \)), meaning they reach peak values simultaneously.


  • In a purely capacitive element, the current leads the voltage by exactly \( 90^\circ \) (\( \frac{\pi}{2}\text{ rad} \)) because charging current must flow onto plates before the potential difference can build up across them (often remembered by the acronym ICE: In a Capacitor, Current leads EMF).


Why other options are incorrect:

  • Options stating that \( I \) and \( V \) are out of phase in a resistor, or that current lags voltage (which describes an inductor instead) in a capacitor, violate these fundamental physical behaviors.

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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