Why does a Rainbow Appears ?

                              

          Due to the process of precipitation in the earth's atmosphere, Water vapor from the clouds converts into water droplets and fall on to the earth's surface. When the water droplets separated from the clouds, These water droplets converts into a sphere shaped small balls. But the outside surface of the water droplets acts as the convex lens i.e., when the light ray falls on this outside surface of the water droplet it bends light inwards and makes it travel inside symmetrical surface of the water droplet. When the light ray travel inside the surface of the water droplet it acts as a concave lens i.e., It bends light ray and travels outward surface of the water droplet. This process happens due to light refracted from the surface of the water droplet.

            Sometimes during the rainfall, Sunlight also get projected due to the little number of clouds present in the Troposphere. This makes to happen sunlight to fall on the earth's surface and rainfall to happen at the same time. Due to this process, Sunlight which falls on the water droplets of the clouds makes the light to get refracted multiple times. Since when light falls on a transparent medium it makes the plain (or) white light into getting dispersed into seven colors i.e., VIBGYOR. These seven colors are called as Spectrum of Light. In the same way, the sunlight gets dispersed from the rainwater droplets. This refracted light separates into seven colors and makes to form as the Rainbow but to the opposite side of the Sunlight.