The diagram is given below:

A rainbow is a band of colors. It is a natural spectrum appearing in the sky after rain. It is formed by the dispersion of sunlight by tiny water droplets in the sky. The water droplets act as tiny prisms. Light strikes the outer surface of the droplets and enter the droplet. Now the light ray strikes the inner surface of the droplet and reflects internally instead of refracting and moving out. Now the internally reflected ray strikes the opposite inner surface of the droplet and now refracts and moves out. This ray is dispersed into rainbow’s colors. Multiple refraction and internal refection gives rise to a rainbow.