How is Colour Formed
Take a CD (compact disc) out in the sun and see how light is reflected from its shining surface. What do you see? Many colours. These colours actually come from the sunlight.
White light is composed of many colours. When these colours combine, they look white. One way of showing that white light is composed of different colours is to make white light pass through a glass prism. This splits up the white light into its constituent colours.
Fig. White light splitting into its constituent colours
If you hold a screen in its path, you will see a band of colours. This band of colours is called the Spectrum. As it is visible to the Red Orange Yellow Green Blue Indigo Violet human eye, it is called the visible spectrum. When light falls on an object, it absorbs a few of these colours and reflects the rest. In case of a green leaf, it absorbs all the colours except green (which it reflects). That is why we see it as green.
Fig. The visile spectrum (VIBGYOR)
Another method which can be used to show that white light is composed of different colours is to show that different colours, when combined, give us white light. This is what happens in a Newton’s disc. Let us learn about it.