Copper and aluminum are being considered for a high-voltage transmission line that must carry a current of 51.5 a. the resistance per unit length is to be 0.144 ω/km. the densities of copper and aluminum are 8960 and 2600 kg/m3, respectively. compute (a) the magnitude j of the current density and (b) the mass per unit length λ for a copper cable and (c) j and (d) λ for an aluminum cable.

a).Jcu= 436.44

b).λcu=1.05728

c).Jal= 274.66

d).λcu=0.487

Explanation:

a).

ζcu=1.7Ωm

ζal=2.76Ωm

wcu=ζcu*l

b).

mass per unit Copper

λcu=Dcu*Acu

λcu=8960 *1.18

λcu=1.05728

c).

wal=ζal*l

d).

mass per unit Aluminum

λal=Dal*Aal

λal=2600 *0.1875

λcu=0.487

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.