Question

Class X Sciences
[papers from previous years]

A narrow beam PQ of white light is passing through a glass prism
ABC as shown in the diagram.
Trace it on your answer sheet and show the path of the emergent
beam as observed on the screen DE.
(i) Write the name and cause of the phenomenon observed.
(ii) Where else in nature is this phenomenon observed ?
(iii) Based on this observation, state the conclusion which can be
drawn about the constituents of white light.

Answer 1

see the diagram

Dispersion of light is the phenomenon of splitting of white light into its constituent colors.  Dispersion happens when white light passes through a glass prism.  The  different colors of light waves have different speeds in any medium like glass.  They have different bending amounts after refraction.  Hence, they show up separately beside each other.

These colors are Violet, indigo, blue, green, yellow, orange, and red.    The rainbow also is formed due to dispersion of light waves at tiny water droplet interface with atmospheric air.  Please see the diagram for the related geometry.

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ii
dispersion of light is observed when some oil spills over water.  We observe colors splitting from refraction from water, oil surfaces.

dispersion is observed after rain during the morning or in the afternoon.
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constituents of light are :  Violet, Indigo,  Blue, Green Yellow Orange and Red colors.