Formation of a Rainbow

When sunlight falls on drops of rain, it undergoes several physical phenomena that result in the formation of a rainbow. These phenomena are:

1. Refraction:
Refraction is the bending of light as it passes from one medium to another. When sunlight enters a raindrop, it undergoes refraction as it transitions from air to water. The speed of light changes as it enters the water, causing the light to bend.

2. Dispersion:
Dispersion is the separation of white light into its constituent colors. White light is made up of different wavelengths, each corresponding to a different color. As light enters the raindrop and undergoes refraction, the different wavelengths of light are bent by different amounts, resulting in the separation of colors.

3. Internal Reflection:
Internal reflection occurs when light is reflected back into the medium it came from, instead of being transmitted through it. As light enters the raindrop and undergoes refraction, some of the light rays reflect off the inside surface of the raindrop. These internally reflected rays then undergo further refraction as they exit the raindrop.

Formation of a Rainbow:
When sunlight enters a raindrop, it undergoes refraction and dispersion. The different colors of light are separated and undergo internal reflection within the raindrop. As the internally reflected rays exit the raindrop, they undergo further refraction and dispersion. The different colors of light are then redirected towards the observer's eye.

The observer sees a circular band of colors, with red on the outside and violet on the inside. This is because the different colors of light are bent at slightly different angles as they exit the raindrop, resulting in the separation of colors. The circular shape of the rainbow is due to the fact that the angle of refraction and reflection within the raindrop is constant.

Conclusion:
In summary, the formation of a rainbow when sunlight falls on drops of rain is a result of refraction, dispersion, and internal reflection. These physical phenomena work together to separate the colors of light and redirect them towards the observer, creating the beautiful phenomenon of a rainbow.