The phenomenon of rainbow formation by water droplets involves:

The formation of a rainbow is a complex optical phenomenon involving the interaction of sunlight with water droplets. When sunlight enters a raindrop, it first undergoes refraction and dispersion as it passes from air into the denser water medium [1]. Inside the droplet, the light is reflected internally off the back surface [2]. Finally, the light undergoes a second refraction as it exits the droplet to reach the observer's eye [1]. While a primary rainbow involves a single internal reflection, a secondary rainbow is formed by two internal reflections [2]. Therefore, the general phenomenon of rainbow formation fundamentally relies on both the refraction and internal reflection of sunlight [2]. This combination of processes separates white light into its constituent colors, creating the visible spectrum in the sky [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > Activity 10.2 > p. 167
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Explanation: > p. 335