Physics - Modern Physics Question with Solution | TestHub

Energy flux = Energy of photons from reaching the earth per second per unit area $\varphi =1.388\times 10^3\mathrm{W}{\mathrm{m}}^{-2}=1.388\times 10^3\mathrm{J}{\mathrm{s}}^{-1}{\mathrm{m}}^{-2}$ Let $n=$ number of photons incident on earth per $\sec {\mathrm{m}}^{-2}$ and $E^{\prime }=$ energy of each photon $=\frac{hc}{\lambda }$ If $E$ be the energy of all photons reaching the surface of earth per sec per unit area, then $\begin{array}{rl}& E=n{E}^{\prime }=\frac{nhc}{\lambda }\\ & \therefore \frac{nhc}{\lambda }=\varphi \text{ or }n=\frac{\varphi }{\left(\frac{hc}{\lambda }\right)}=\frac{1.388\times 10^3}{hc}\times \lambda \end{array}$ $=\frac{1.388\times 10^3\times 550\times 10^{-9}}{6.62\times 10^{-34}\times 3\times 10^8}=3.85\times 10^{21}$