Explain the process of rainbow formation, including the roles of refraction, reflection, and dispersion.

A rainbow forms when sunlight interacts with water droplets in the atmosphere. The process involves three main optical phenomena: refraction, reflection, and dispersion.

When sunlight enters a spherical water droplet, it first undergoes refraction, bending as it passes from air into water. Inside the droplet, the light then hits the back surface and is reflected internally. Finally, as the light exits the droplet, it undergoes a second refraction, bending again as it passes from water back into the air.

During both refractions, the white sunlight is dispersed into its constituent colors (the spectrum: red, orange, yellow, green, blue, indigo, violet). This happens because different wavelengths (colors) of light bend at slightly different angles. Red light bends the least, and violet light bends the most.

An observer sees a rainbow when their back is to the sun and they are facing the rain. Each water droplet acts like a tiny prism, sending specific colors of light back to the observer's eye at particular angles. The combined effect of millions of droplets, each refracting, reflecting, and dispersing light, creates the arc of colors we perceive as a rainbow.