6 April 2014

Sunlight & Rainbow


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. The centre of the rainbows arc is always directed away from 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.  
A rainbow lasted for about 9 hours on 14th March, 1994, at a place called Wetherby in Yorkshire, England.  
Although sunlight appears white, it is composed of seven colours. The colours in a rainbow are the colours of sunlight. 
A rotating disc has a pencil that serves as a rotator. The disc is covered with violet, indigo, blue, green, yellow, orange and red coloured papers.
Sunlight, Rainbow, CBSE Notes, Class 7, NCERT NotesWhen the disc is rotated, it appears white instead of the individual colours. This is because a mixture of colours of the rainbow in proper proportions produces white colour. 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

Take a glass prism. Allow a narrow beam of sunlight to pass through a small hole in the window of a dark room to fall on one face of the prism. The light bends when it passes through the prism. Now allow the light coming out of the other face of the prism 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.

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