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

Question

$\begin {array} {1 1} (a)\;3.84 \times 10^{20}photons/m^2/s & \quad (b)\;38.4 \times 10^{21}photons/m^2/s \\ (c)\;0.384 \times 10^{20}photons/m^2/s & \quad (d)\;3.84 \times 10^{21}photons/m^2/s \end {array}$