Rainbows are the one of the finest, most magnificent and incredible phenomenon that nature has to offer. The formation of rainbow as a phenomenon includes and consists of extensive and complex physics. It demonstrates some of the most intricate processes in Physics like dispersion of light and also proves that visible light is composed of a spectrum of wavelengths and each of these wavelengths is associated to a different color.
Two physical phenomena that are at work within a rainbow are refraction and reflection. Both hold their significance when it comes to formation of rainbows. Refraction occurs each and every time when light passes across a boundary from one substance to another, such as from air to water (Field 2011). In case of Rainbows a collection of suspended water droplets in the atmosphere are responsible for refraction of light. Since the optical density of water differs from that of air, light ways refract when they cross over the boundary, in this case from air to water. Since water has higher optical density as compared to the air, the ray of light bends towards the normal when it crosses over and when the light exits the water droplet, it speeds up since it moves from a medium of higher optical density to a one of lower optical density and hence it moves away from the normal. The process of refraction when the light enters and exits water droplets causes deviation in the path of light.
There are countless and numerous paths by which light rays from the sun pass through a drop, but the most significant and the one primarily responsible for the formation of Rainbows is the path in which the ray of light refracts into the droplet, internally reflects and then refracts out of the droplet. Upon refracting twice and reflecting once, the light day is dispersed and bent downwards towards an observer on earth’s surface (physicsclassroom 2013). As observed in the case of refraction of light through prism, the refraction of light at the boundaries of the suspended water droplets results in dispersion of light into spectrum of colors.
The rainbow is often seen as a circle or semi circle and it results because of the huge collection of suspended water droplets, which are capable of concentrating the dispersed light (after double refractions and internal reflection) at angle of deviation of 40-42 degrees to the initial paths. Every droplet refracts and disperses the entire light spectrum (ROYGBIV). These types of rainbows, which are formed between 40 and 42 degrees of the antisolar point, are called Primary Rainbows.
Secondary Rainbows are a formed around 10 degrees of the antisolar point unlike the primary rainbows, which are formed between 40 and 42 degrees. Secondary rainbows are wider when compared to primary rainbows but have very less intensity. The main feature that sets them apart from primary rainbows is the fact that they have colors reversed. They involve two reflections inside the water droplet. These two internal reflections cause the rays to be deviated by more than 180 degrees and the light finally emerges as the secondary bow. The deviation of over 180 degrees results in reversing of colors.
Both the primary and secondary rainbows involve some of the finest concepts of physics. Reflection and refraction both play their parts in the formation of rainbows. The dispersion of the light into different colors based on the wavelengths produces different colors. The rainbow, a natural phenomenon that is a teat to eyes, has a very scientific formation and existence.
References
Field, Tom. ”The Physics: How a Rainbow forms”
Photo centric. 21 April 2013. Web. 2011
< http://www.photocentric.net/rainbow_physics.htm>
Physicsclassroom. ”Rainbow formation”
The Physics Classroom. 21 April 2013. Web. 2013
< http://www.physicsclassroom.com/Class/refrn/u14l4b.cfm>
