Question

Energy received by earth from sun is 1.4×10^3 j/ m^2-s . If average wavelength of sunlight is 5500 ×10^-10 , how many photons are coming from sun to erath per second per cm^2 ?

Answer 1

Ans :- 22^6 Photons.

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Answer 2

Index :-

$N_P=Number\ of\ incident\ photons$

$h=Plancks\ Constant$

$c=Speed\ of\ light$

${\lambda}=Incident\ wavelength$

$T=Time$

$A=Area$

$I=Intensity\ of\ sunglight\ reaching\ on\ the\ earth\ surface$

Solution :-

Energy flux is equivalent to intensity.

Intensity of sunlight reaching the earth surface (I) is

$=\frac{(Number\ of\ photons\ emitted)(Energy\ of\ 1\ photon)}{(Time)(Area)}$$=\frac{(Number\ of\ photons\ emitted)(\frac{hc}{ \lambda }) }{(Time)(Area)}$

$=\frac{(N_P)(\frac{hc}{\lambda}) }{(T)(A)}$

$=>N_P=\frac{(I)(T)(A)(\lambda)}{hc}$

$=>N_P=\frac{((1.4\times10^3)W/m^2)((1)s)((1)m^2)((550)nm)}{((1240)eV.nm)}$

$=>N_P=3.85\times10^{21}$

Hence, number of photons incident on the Earth per second/square meter are 3.85 × 10²¹.

Remarks :-

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