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 :
A
3×1019
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B
9×1017
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C
3×1016
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D
9×1015
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Solution
The correct option is D3×1016 No.ofphotons=E(hc/λ) =9×10−3×6.67×10−76.6×10−34×3×108 =3×1016