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 $550 \; nm$.

  • A
    $9 \times 10^{22} \; \text{photons}/m^{2} \cdot s$
  • B
    $6 \times 10^{22} \; \text{photons}/m^{2} \cdot s$
  • C
    $8 \times 10^{20} \; \text{photons}/m^{2} \cdot s$
  • D
    $4 \times 10^{21} \; \text{photons}/m^{2} \cdot s$

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