By Yeoh Li Yuan (2O2/33) Term3 LSS ACE Formation of Rainbow

How is rainbow formed Rainbow is formed when a light passed through water droplet and refracted to the sky When the light passed through water droplet, it is separated into its component colours  red, orange, yellow, green, blue and violet. The separation of light is known as dispersion of light. So, the rainbow that we seen are made of these colours and it is always in this order.

Introduction to light dispersion Visible light, also known as white light, consists of a collection of component colours. These colours are observed as light passes through a triangular prism. Upon passing through the prism, the white light is separated into its component colours - red, orange, yellow, green, blue and violet. The separation of visible light into its different colours is known as dispersion. Picture of a white light passing through a triangular prism Did you know? The one who found out this is Isaac Newton.

Refraction and reflection of light in water droplet Light waves refract when they cross over the boundary from one medium to another. The decrease in speed upon entry of light into a water droplet causes a bending of the path of light towards the normal. And upon exiting the droplet, light speeds up and bends away from the normal. The droplet causes a deviation in the path of light as it enters and exits the drop. There are countless paths by which light rays from the sun can pass through a drop. Example is on next page 

A diagram on refraction of light in water droplet Explanation: A light ray from the sun enters the droplet with a slight downward trajectory. Upon refracting twice and reflecting once, the light ray is dispersed and bent downward towards an observer on earth's surface. Other entry locations into the droplet may result in similar paths or even in light continuing through the droplet and out the opposite side without significant internal reflection.

Maximum angle at which light should leave droplet to see the rainbow Something you must know: Each individual droplet of water acts as a tiny prism that both disperses the light and reflects it back to our eye. As our sight into the sky, wavelengths of light associated with a specific color arrive at our eye from the collection of droplets. Also, rainbow is most often viewed as a circular arc in the sky. An observer on the ground observes a half-circle of color with red being the color perceived on the outside or top of the bow. This is because there are a collection of suspended droplets in the atmosphere that are capable concentrating the dispersed light at angles of deviation of degrees relative to the original path of light from the sun. Solution is on next page 

Maximum angle at which light should leave droplet to see the rainbow So, to view a rainbow, our back must be to the sun as we look at an approximately 40 degree angle above the ground into a region of the atmosphere with suspended droplets of water or even a light mist. It is impossible for an observer to maneuver to see any rainbow from water droplets at any angle other than the customary one, which is 42 degrees from the direction opposite the sun.

An example for maximum angle to view a rainbow

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