Question

Describe an experiment to show that white light consists of lights of different colours.

Answer 1

Take two identical prisms P1 and P2 as shown in the figure below. Keep the second prism P2 in an inverted position with respect to the first prism. Allow a narrow beam of white light to fall on first prism P1.


The first prism P1 disperses the white light into seven colours because of refraction, when there is a change in the medium.
These seven colours is received by the second prism P2, and recombines them into white light. Thus a beam of white light emerges from the other side of the second prism. Hence, the seven colors that are dispersed can be again re-combined into white light.

This observation gave Newton the idea that the sunlight is made of seven colours.
Any light that gives a spectrum similar to that of sunlight is called white light.

Answer 2

We can perform Newton's prism experiment to demonstrate that white light consists lights of different colours.

Explanation:

• Take a glass prism which is generally used in physics experiments
• Place it on a plane white paper
• Make a pinhole in a cardboard or any other hard material
• Allow a source of white light to pass through that pin hole and let it fall on one inclined side of the prism
• You will notice that white light has spread into seven colours on the white sheet
• Hence , you can demonstrate that white light consists of seven colours i.e violet, indigo, blue, green, yellow, orange and red.

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