Dual Nature of Matter

JEE Main level, single correct, medium

119 of 200

Question 119 of 200

Monochromatic light of frequency 6×1014Hz6\times {10}^{14}Hz is produced by a laser. The power emitted is 2×10−3W.2\times {10}^{-3}W. How many photons per second on an average, are emitted by the source?
(Given h=6.63×10−34Jsh=6.63\times {10}^{-34}Js)

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Answer: (C) 5×10155\times {10}^{15}

Energy of a single photon is given by, hνh\nu. Therefore, power can be written as
P=nhvP=nhv
⇒n=Phν=2×10−36.63×10−34×6×1014\Rightarrow n=\dfrac{P}{h\nu }=\dfrac{2\times {10}^{-3}}{6.63\times {10}^{-34}\times 6\times {10}^{14}}
=5×1015=5\times {10}^{15}

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