Question
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:
BITSAT
Physics
Dual Nature of Matter
2021
BITSAT 2021
BITSAT Physics Question (2021) — Solution
Options
- A. 3 10^ 16
- B. 9 10^ 15
- C. 3 10^ 19
- D. 9 10^ 17
Answer
A. 3 10^ 16
Step-by-step solution
=667 10^ -9 m, P =9 10^ -3 ~W P = Nhc , N = No. of photons emitted/sec. N = 9 10^ -3 667 10^ -9 6.6 10^ -34 3 10^ 8 =3 10^ 16 / sec
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