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Activity on dispersion of light

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  • Take a thick sheet of cardboard and make a small hole or narrow slit in its middle.
  • Allow sunlight to fall on the narrow slit. This gives a narrow beam of white light. 
  • Now, take a glass prism and allow the light from the slit to fall on one of its faces.
  • Turn the prism slowly until the light that comes out of it appears on a nearby screen . W
  • What do you observe? You will find a beautiful band of colours. Why does this happen?

The prism has split the incident white light into a band of colours. The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR). The band of the coloured components of a light beam is called its spectrum.

Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most. Thus the rays of each colour emerge along different paths and thus become distinct.

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