Physics Dawn of Modern Physics SZABMU 2022
PMDC Verified Question 27 of 52
Red light is used in photographic dark room because of:
A
More frequency, less wavelength
B
Less frequency, less wavelength
C
Less frequency, more wavelength
D
More frequency, more wavelength
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Less frequency, more wavelength
Concept:

Photographic paper is coated with light-sensitive chemicals (like silver halides) that react when struck by photons with energy above a certain threshold.

Formula:

$$ E = hf = \frac{hc}{\lambda} $$

Solution:

  • To avoid ruining the developing photos, a darkroom must use light whose individual photons lack the energy to trigger the chemical reaction.


  • Red light sits at the far end of the visible spectrum.


  • It has the longest wavelength and consequently the lowest frequency, meaning its photons carry the least energy.


Why other options are incorrect:

Options claiming "More frequency" or "less wavelength" would describe energetic light like blue or violet, which would instantly expose and ruin photographic paper.

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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