Question

The energy flux of the sunlight reaching the surface of the earth is `1.388xx10^(3) W m^(-2)`. How many photons (nearly) per square meter are incident on the earth per second? Assume that the photonsin the sunlight have an average wavelength of 550 nm.

Answer 1

Here, energy flux (energy per second per unit area) of sunlight reaching the surface of the earth,
`phi=1.388xx10^3Wm^-2`
`lamda=550nm=550xx10^-9m` Therefore, energy of a photon of sunlight,
`E=(hc)/(lamda)=(6.62xx10^-34xx3xx10^8)/(550xx10^-9)=3.61xx10^-19J`
Therefore, the number of protons emitted per second is
`(1.388xx10^3)/(3.61xx10^-19)=3.845xx10^21s^-1`