colours Archives

What is Newton’s Disc

Newton’s disc is a coloured disc which is painted with the colours of white light [i.e., violet, indigo, blue, green, yellow, orange, and red (VIBGYOR)] in equal proportions so that when it is rotated very fast, the disc appears white. This is because of a property of our eyes called persistence of vision. This means that an image formed by the eye remains for a fraction of a second. When the disc is rotated at a high speed, the images of the different colours overlap in our eyes and the brain perceives it as white.

Newton’s Disc

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.
How is Colour Formed 1

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.
How is Colour Formed 2

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.