AIPMT MAINS2009Physics-Optics
AIPMT MAINS 2009 Physics Photon Energy MCQ Question
Type: MCQ-numerical-Medium-Class 12
Monochromatic light of wavelength 667 nₘ is produced by a helium neon laser. The power emitted is 9 mW. The number of photons arriving per sec. On the average at a target irradiated by this beam is:
A
3 × 10¹⁶
B
9 × 10¹⁵
C
3 × 10¹⁹
D
9 × 10¹⁷
Correct Answer
Option A
Detailed Explanation
The energy of a photon is given by E = hc/λ. The number of photons per second is the power divided by the energy per photon. Substituting the values, the number of photons is approximately 3 × 10¹⁶.
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