The left end of a long glass rod, 8.00cm in diameter, has a convex hemispherical surface 4.00cm in radius. the refractive index of the glass is 1.60.
a) determine the position sb of the image of an object placed in air on the axis of the rod infinitely far from the left end of the rod. sb=

b) determine the position sb of the image if an object is placed in air on the axis of the rod 18.0cm to the left of the end of the rod. sb=

c) determine the position sb of the image if an object is placed in air on the axis of the rod 4.00cmfrom the left end of the rod. sb=

hypothesising or postulating

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.