The intensity of electromagnetic radiation from the sun reaching the earth's upper atmosphere is 1.37kW/m2kW/m2. Part A Assuming an average wavelength of 680 nmnm for this radiation, find the number of photons per second that strike a 1.50 m2m2 solar panel directly facing the sun on an orbiting satellite.

#_photon = 7  10²¹ photons

Explanation:

Let's look for the power that affects the panel of area of 1.5 m2

           I = P / A

           P = I A

           P = 1.37 10³  1.5

           P = 2,055 10³ W

           P = E / t

If we use t = 1 s

           E = P t

           E = 2,055 10³ J

This is the power that the panel receives, let's look for the energy of a photon

            E = h f

            c = λ f

            f = c /λ

            E = h c /λ

Let's calculate

            E₀ = 6.63 10⁻³⁴  3 10⁸/680 10⁻⁹

            E₀ = 2.925 10⁻¹⁹ J

In one second the total energy is the number of photons for the energy of each one

             E = #_photon  E₀

             #_photon = E / E₀

             #_photon = 2,055 10³ / 2,925 10⁻¹⁹

            #_photon = 7  10²¹ photons

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.