10.4 DISPERSION OF WHITE LIGHT BY A GLASS PRISM · Part 2

by using another similar prism. However, he could not get any more colours. He then placed a second identical prism in an inverted position with respect to the first prism, as shown in Fig. . . This allowed all the colours of the spectrum to pass through the second prism. He found a beam of white light emerging from the other side of the second prism. This observation gave Newton the idea that the sunlight is made up of seven colours. Any light that gives a spectrum similar to that of sunlight is often referred to as white light. A rainbow is a natural spectrum appearing in the sky after a rain shower (Fig. . ). It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop (Fig. . ). Due to the dispersion of light and internal reflection, different colours reach the observer’s eye. You can also see a rainbow on a sunny day when you look at the sky through a waterfall or through a water fountain, with the Sun behind you. Figure . Dispersion of white light by the glass prism Figure . Recombination of the spectrum of white light Figure . Rainbow in the sky Figure . Rainbow formation Sunlight Raindrop Atmospheric refraction effects at sunrise and sunset