IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Dispersion of Light by a Prism

Procedure

Make a narrow slit on a stiff piece of paper and make it stand vertically. Allow sunlight or torchlight to fall on the slit, to create a narrow beam of light. Let this beam fall on a rectangular face of a prism placed near a wall. Light will pass through the prism and fall on the wall. Rotate the prism till you see a band of colours on the wall.

Dispersion of light using a Water and Plane Mirror: Get a plane mirror of suitable size. Place it in a bowl (Katori) as shown in figure. Fill the bowl with water. Put this arrangement near a window such that direct sunlight falls on the mirror. Adjust the position of the mirror such that the reflected light from the mirror falls on a wall. If the wall is not white, fix a sheet of white paper on it. Reflected light will be seen to have many colours. How can you explain this? The mirror and water form a prism. This split the light into multiple colours. Splitting of light into its colours is known as dispersion of light. Rainbow is a natural phenomenon showing dispersion.