Question

Draw a ray diagram to show the formation of a rainbow. Mark on it, points (a), (b) and (c) as given below: 
(a) Where dispersion of light occurs. 
(b) Where light gets reflected internally. 
(c) Where final refraction occurs.

Hint:

Rainbows occur due to the dispersion of light, which is then reflected internally inside water droplets before exiting and forming a spectrum of colors.

Answer 1

The formation of a rainbow occurs when sunlight is refracted and dispersed through water droplets in the atmosphere. The diagram of rainbow formation consists of the following steps: 
Dispersion of light (Point a): As the sunlight enters the water droplet, it bends or refracts due to the change in medium. Since different colors of light have different wavelengths, they refract by different amounts, resulting in dispersion (splitting of white light into its constituent colors). 
Internal reflection (Point b): After dispersion, the light travels through the water droplet and strikes the inner surface of the droplet. The light gets reflected internally at the back of the droplet, which is the cause of the rainbow's curved appearance. 
Refraction again (Point c): After internal reflection, the light exits the droplet. As it exits, the light refracts again, further separating the colors and creating the visible spectrum of light (the rainbow). The final rainbow seen by the observer is a result of multiple droplets refracting, reflecting, and refracting again, each displaying different colors at different angles.