Q. Monochromatic light of frequency 6.0 × 10¹⁴ Hz is produced by a laser. The power emitted is 2 × 10⁻³ W. The number of photons emitted, on the average, by the sources per second is
A) 5 × 10¹⁶
B) 5 × 10¹⁷
C) 5 × 10¹⁴
D) 5 × 10¹⁵
Explanation
[Solution from source] n = P/(hf) = 2 × 10⁻³/(6.63 × 10⁻³⁴ × 6.0 × 10¹⁴) = 2 × 10⁻³/3.98 × 10⁻¹⁹ ≈ 5 × 10¹⁵ per second. 5 × 10¹⁶ is a power-of-ten slip. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.