Physics Alternating Current SZABMU 2025
PMDC Verified Question 75 of 127
A capacitor is connected to an ac source. If the frequency of the AC source is doubled the current in a purely capacitive circuit will:
A
Remains Unchanged
B
Be doubled
C
Become Half
D
Becomes 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: Be doubled
Concept:

In a purely capacitive AC circuit, the alternating current is directly proportional to the supply frequency because capacitive reactance decreases as frequency rises.

Formula / Reaction:

$$I = \frac{V}{X_C} = 2\pi f C V$$

Solution:

  • The reactance of a capacitor is given by \(X_C = \frac{1}{2\pi f C}\).


  • The alternating current is \(I = \frac{V}{X_C} = V(2\pi f C) = 2\pi f C V\).


  • Since \(I \propto f\), doubling the source frequency (\(f' = 2f\)) directly doubles the current in the circuit (\(I' = 2I\)).


Why other options are incorrect:

Increasing frequency reduces capacitive opposition to current flow; hence, current cannot remain unchanged, halve, or drop 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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