A band of colours extending from violet to red is a rainbow
. A rainbow is formed by the refraction and reflection of the sun’s rays through raindrops. When it is raining in one part of the sky and sunny in another, a rainbow appears. An observer can therefore see a rainbow only when his back is towards the sun. It is believed that in the past, Norsemen saw rainbows as bridges for gods to come to the earth from their home in the sky. Norsemen were the inhabitants of Norway.
Although sunlight appears white, it is composed of seven colours. The colours in a rainbow are the colours of sunlight
A Newton's disc can be created by painting a disc with the seven different colours: violet, indigo, blue, green, yellow, orange and red. When the disc is rotated, it appears white. This explains that white light consists of seven colours. The colours of a rainbow can be represented by the acronym: VIBGYOR: V – Violet, I - Indigo, B – Blue, G – Green, Y - Yellow, O - Orange and R - Red.
Dispersion of Light Through a Prism
When a narrow beam of light is incident on one face of a glass prism
, light bends when it passes through the prism. Now the light coming out of the other face of the prism is made to fall on a white sheet of paper or a white wall. Different component colours of white light bend differently, and so the constituent colours can be seen separately. Thus, the colours are said to have dispersed after passing through the prism.