How many photons are there in each cubic meter near the earth's surface at any instant?

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Solution

Total number of photons emitted in time $d t = n d t$ where $d t = \frac{d r}{c}$ where dr and c are the displacement and
speed of light.
Now number of photons per unit volume $= \frac{P π d r}{h C^{2}}$
$\frac{P λ}{4 π r^{2} C h}$ where $\frac{P}{4 π r^{2}}$ =1.4 $\times$ $10^{3}$ and $λ$ = $5000 ˚ A$
$= 1.4 \times 10^{3} (\frac{5 \times 10^{- 7}}{6.63 \times 10^{- 34} \times 3 \times 10^{8}}) = 3.51 \times 10^{21}$

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How many photons are there in each cubic meter near the earth's surface at any instant?

Total number of photons emitted in time dt=ndt where dt=drc where dr and c are the displacement and speed of light.Now number of photons per unit volume =PπdrhC2 Pλ4πr2Chwhere P4πr2=1.4×103 and λ=5000˚A=1.4×103(5×10−76.63×10−34×3×108)=3.51×1021