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Monochromatic light of wavelength 3000 Å...

Monochromatic light of wavelength 3000 Å is incident normally on a surface of area 4`cm^(2)` If the intensity of light is 150`(m W)/(m^(2))`, the number of photon being incident on this surface in one second is ……

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`lambda=3000Å =3xx10^(-7)m`
`A=4cm^(2)=4xx10^(-4)m^(2)`
`I=150(mW)/(m^(2))=150xx10^(-3)(W)/(m^(2))`
`h=6.62xx10^(-34) Js`
`"intensity" I=(E )/(Axxt)=(P)/(A)`
`therefore P=IA=150xx10^(-3)xx4xx10^(-4)` If number of photon colliding on the surface are n,its energy =power `P=(nhc)/(lambda)`
`therefore n=(plambda)/((hc))=(6xx10^(-5)xx3xx10^(-7))/(6.62xx10^(-34)xx3xx10^(8))`
`therefore n=9xx10^(13)s^(-1)`
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