Question

using the concept of refraction and internal reflection explain how rainbow work

Answer 1

Answer :

Formation of Rainbow :

When light from the sun hits a water droplet, some of the light is reflected. This light will obey the Law of Reflection.

The light that is not refracted crosses the air-water interface (boundary layer). When this happens it slows down because the water is more dense than the air. The reduction of speed cause the path of the light to bend - this is called refraction. In this case the path of the light rays bends toward the normal line.

White light is made up of a spectrum of colours, each with its own wavelength. Different wavelengths travel at different speeds and when they encounter a change to medium that is more dense or less dense, the speeds are efected by different amounts. Hence, the colours separate. This phenomenon is know as Dispersion.

At the rear of the raindrop, the light hits the water-to-air interface. If the angle of incidence is greater than the critical angle, Total Internal Reflection will occur. A rainbow will only be seen if this happens, otherwise the light will continue out the other side of the raindrop and continue to move away from the would-be viewer.

Just as the light changed speed as it entered the raindrop, its speed changes again as it leaves. Here, the light is moving from a more dense medium (water) to a less dense medium (air). As it does so, it speeds up and its path bends. In this case the path of the light rays bends away from the normal line. This is another example of refraction.

As the rays are refracted once again, the various wavelengths are effected to different extents. The overall result of this is increased separation of the component colours of white light. This is Dispersion.

Thus the rainbow is formed by Combined effect of : Refraction, Total internal reflection and Dispersion of light.