Infinity Science study: What is Rainbow,Primary Rainbow, Secondary Rainbow.

WHAT IS RAINBOW?? STATE CONDITIONS FOR OBSERVING RAINBOW.

Rainbow is the beautiful illustration of dispersion of light and is observed during the rainfall or after rainfall or when we look at a water fountain provided the sun is shining at back of the observer (Condition for observing Rainbow).

Rainbow is formed due to the dispersion of light, refraction and total internal reflection of light in the droplets present in the atmosphere. Thus, Rainbow is combined effect of refraction, total internal reflection and dispersion of light.

Sometime two rainbows are seen. The inner rainbow is called Primary Rainbow and the outer one is called Secondary Rainbow.

PRIMARY RAINBOW:

When sun light fall on a water drop suspended in air, then part of light is reflected and part of light is refracted. The refracted light is dispersed (or splits) into its constituent colours. Thus, the water drop suspended in air act as glass prism. The red colour is deviate least and the violet colour is deviated the most. Different colours of refracted sunlight fall on opposite side of the drop. Now each colour suffers total internal reflection. The reflected colour on reaching the lower surface of water drop suffers another refraction. The refracted colours gives rise to spectrum called Primary Rainbow. 

Thus primary Rainbow is formed due to two refractions, one total internal reflection and another is dispersion is light by the droplets (tiny water drop) suspended in the air. The outer edge of the primary  Rainbow is red and the inner edge is violet.

An observer can see the red colour of the Rainbow if the angle between the beam of the sunlight and the light coming outer of the drop is 42 degree. However, the observer sees the violet colour of the rainbow when angle between the beam of sun light and light coming outer of the drop is 40 degree.

SECONDARY RAINBOW:

It is formed due to refractions, two internal reflection and dispersion of light by the droplets suspended in air.

Secondary rainbow is coloured band having violet colour on outer side and red colour on the inner side.