Question

The energy flux of sunlight reaching the surface of the earth is $1.388\times {10}^{3}W/m^2$. How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.

Answer 1

Power of sunlight per $m^2=P=1.388\times {10}^{3}W/m^2$

Average $\lambda =550\times {10}^{-9}m$

Let $n$ be no. of photons per $m^2$ incident on earth per second.

$P=nE;E=hc/\lambda \Rightarrow n=3.84\times {10}^{21}photons/m^2/s$