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A monochromatic source of light operatio...

A monochromatic source of light operation at 200 W emits `4xx10^(20)` photons per second. Find the wavelength of the light `"(in" 10^(-7)m`).

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The correct Answer is:
D
The energy of each photon is `(200J//S)/(4xx10^(20)//s)=5xx10^(-19) J` Wavelength =`lambda=(hc)/E`
`((6.63xx10^(-34)J-s)xx(3xx10^(8)m//s))/((5xx10^(-19)J))=4.0xx10^(7) m`
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