Physics Alternating Current ETEA 2015
PMDC Verified Question 108 of 127
At what frequency will a \(1\text{ H}\) inductor have a reactance of \(500\ \Omega\)?
A
80 Hz
B
60 Hz
C
40 Hz
D
20 Hz
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: 80 Hz
Concept:

Inductive reactance is related to frequency and inductance by \(X_L = 2\pi f L\).

Formula / Reaction:

$$f = \frac{X_L}{2\pi L}$$

Solution:

  • Given: \(X_L = 500\ \Omega\) and \(L = 1\text{ H}\).


  • \(f = \frac{500}{2\pi(1)} = \frac{250}{\pi} \approx \frac{250}{3.1416} \approx 79.6\text{ Hz} \approx 80\text{ Hz}\).


Why other options are incorrect:

  • Opt_B: \(60\text{ Hz}\) gives \(X_L \approx 377\ \Omega\).


  • Opt_C: \(40\text{ Hz}\) gives \(X_L \approx 251\ \Omega\).


  • Opt_D: \(20\text{ Hz}\) gives \(X_L \approx 126\ \Omega\).

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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