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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:
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- 3 × 1016
- 9 × 1015
- 3 × 1019
- 9 × 1017
Correct Option: A
λ = 667 × 10-9 m,
P = 9 × 10-3 W
| P = | λ |
N= No. of photons emitted/sec.
| N = | 6.6 × 10-34 × 3 × 108 |
| = | ≃ 3 × 1016/sec | 3 × 6.6 × 10-26 |
