The phenomenon of rainbow formation by water droplets involves :

The correct answer is  both refraction and internal reflection of sunlight.

Key PointsRainbow Formation by Water Droplets

• Refraction: When sunlight enters a water droplet, it slows down and bends. This bending of light is called refraction. The light is refracted at the surface of the droplet.
• Internal Reflection: After refraction, the light reflects off the inside surface of the water droplet. This internal reflection is crucial to the formation of a rainbow.
• Second Refraction: The light undergoes a second refraction as it exits the droplet, bending again as it moves from water to air.
• Dispersion: During these processes, the light is dispersed into its constituent colors (spectrum) due to different wavelengths of light bending by different amounts.
• The combination of these processes - refraction, internal reflection, and dispersion - results in the formation of a rainbow.

Additional Information

• Refraction: This is the bending of light as it passes from one medium to another. The amount of bending depends on the indices of refraction of the two media and the wavelength of the light.
• Internal Reflection: Occurs when light hits the boundary of a medium and is reflected back into the medium instead of passing through. This is essential for the formation of a rainbow.
• Dispersion: The process in which white light separates into its constituent colors (spectrum) due to different degrees of bending for different wavelengths. This is why rainbows display a spectrum of colors.
• Rainbow Colors: The colors of a rainbow typically include Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROYGBIV), arranged in this order from the outer to the inner edge of the rainbow.
• Viewing Angle: A rainbow is typically seen when the sun is low in the sky and the observer has their back to the sun. The angle of view is approximately 42 degrees relative to the direction opposite to the sunlight.