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Monochromatic light of frequency 6.0xx10...

Monochromatic light of frequency `6.0xx10^(14)` Hz is produced by a laser. The power emitted is `2.0 xx10^(-3)` W(a) What is the energy of a photon in the light beam ? (b ) How many photons per second , on an average , are emitted by the source ?

Text Solution

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Each photon has an energy
` E = hv = (6.63xx 10^(-34) J s)(6.0 xx10^(14) Hz)`
` = 3.98 xx 10^(-19)` J
If N is the number of photons emitted by the source per second , the power P transmitted in the beam equals N times the energy per photon E, so that P = N E
Then N ` P/E = (2.0 xx 10^(-3)W)/(3.98 xx 10^(-19)J)`
` = 5.0 xx10^(15)` photons per second
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