Read the following paragraph and answer the questions given below :Rainbow is a beautiful natural phenomenon. It is the combined effect of dispersion, refraction and total internal reflection of light. It can be seen mainly after rainfall. Small drop…

Answer: (a) Refraction, dispersion and total internal reflection; (b) light bends when it passes from one medium to another with a different optical density; (c) diagram described below.

(a) The three phenomena are refraction, dispersion and total internal reflection of sunlight inside water droplets.

(b) Refraction is the change in direction of light when it travels obliquely from one transparent medium into another in which its speed is different. On entering a water droplet from air the light slows down and bends towards the normal; on leaving the droplet it speeds up and bends away from the normal.

(c) Diagram: draw a large circle for a water droplet with the sun’s rays entering at the upper left. Show the ray being refracted and split into colours at entry, reflected once at the inner back surface, and refracted again as it leaves the lower part of the droplet. Mark red emerging at a larger angle and violet at a smaller angle, with the observer standing with his back to the sun.