Physics Dawn of Modern Physics PMDC 2021
PMDC Verified Question 40 of 52
If velocity Becomes 5 times, what happened to De Broglie Wavelength
A
Increase by 5 times
B
Decrease by 5 times
C
Both
D
None
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Decrease by 5 times
Concept:

The de Broglie wavelength of a moving massive particle is strictly inversely proportional to its velocity.

Formula:

$$ \lambda = \frac{h}{mv} $$

Solution:

  • Because velocity \( v \) is in the denominator, increasing it proportionally shrinks the wavelength.


  • If the new velocity \( v' = 5v \), then the new wavelength is \( \lambda' = \frac{h}{m(5v)} = \frac{1}{5}\lambda \).


  • Thus, the wavelength decreases by a factor of 5.


Why other options are incorrect:

Assuming a direct proportionality would mistakenly lead to "Increase by 5 times". Wavelength and velocity scale oppositely.

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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