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 second on the average at a target irradiated by this beam is

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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 second on the average at a target irradiated by this beam isNEET 2009 (Screening)

TestHub · Accepted Answer

Here λ = 667 × 1 0 − 9 m , P = 9 × 1 0 − 3 W Power ​ = time energy ​ = λ t nh c ​ = λ N h c ​ ​ where is number of photons emitted per sec. ⇒ N ​ = hc P × λ ​ = 6.6 × 1 0 − 34 × 3 × 1 0 8 9 × 1 0 − 3 × 667 × 1 0 − 9 ​ = 3 × 1 0 16 / s ​

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