Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 51 of 127
How many times per second does an incandescent light bulb connected to a standard \(50\text{ Hz}\) AC domestic supply reach maximum brilliance?
A
25 times
B
50 times
C
100 times
D
200 times
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 100 times
Concept:

Instantaneous power dissipated in a light bulb filament is \(P(t) = i^2(t) R\). Current reaches peak magnitude twice per AC cycle (positive peak and negative peak).

Formula / Reaction:

$$\text{Frequency of brightness peaks} = 2f$$

Solution:

  • In each cycle of AC, current reaches a maximum value twice (at \(T/4\) and \(3T/4\)).


  • Because heating \(P = i^2 R\) depends on the square of current, brilliance peaks twice per cycle.


  • Number of peaks per second: \(2 \times 50\text{ Hz} = 100\text{ times/second}\).


Why other options are incorrect:

  • Opt_A: \(25\text{ times}\) is half the frequency.


  • Opt_B: \(50\text{ times}\) counts only positive peaks.


  • Opt_D: \(200\text{ times}\) represents four peaks per cycle.

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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