Reflection, diffraction and refraction are the phenomenon involved in the formation of rainbow. White light from the sun enters the top surface of the water droplet. Due to refraction, the sunlight disperses into seven colours & strikes the surface of droplet at point C. At point C, the angle formed by incident ray is greater than the critical angle. Therefore , total internal reflection occurs at point C and the dispersed spectrum of lights are reflected at the bottom surface of the droplet. At point D, the spectrum again experiences refraction and as they are travelling from denser to rarer medium, the angle between red & violet increases as compared to the angle for the first refraction. There is one more condition, that is, bright rainbow is seen only when the angle between the incoming & the outgoing rays have the maximum angle of 42 degrees.