Total energy = Power x Time(in sec)
= [tex]21 \times 10^{-3} \times 3 \times 3600[/tex] = 226.8 J
Total photons = 4.53 x 10^{20}
Energy per photon = Total energy / Total photon = 50.6 x 10^{-20} J
So, Applying the formula:
E = hc / lambda
lambda = hc / E
Planck constant h = 6.626×10^-34 J s;
c = speed of light = 3×10^8 m s-1
λ = (6.626×10^-34)×(3×10^8)/ 50.6 x 10^{-20} = 0.39 ×10^-6 m= 0.39 um
