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State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms, show that white light is made of seven colours ? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination.

 

 

 

 
 
 
 
 

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Newton's experiment with two identical prisms: . When a beam of white light is passed through a glass prism, a band of seven colors is formed on a white screen. ... Newton showed that the seven colored lights of the spectrum can be recombined to give back white light

The cause of dispersion is the change in speed of light with wavelength .when white light enters the first surface of a Prism ,light of different colours due to their different speeds in glasses gets deviated towards the base of the prism through different angles that is the Dispersion of white light into its constituent colours takes place at the first surface of prism.

Newton's experiment -


Newton allowed white light from the sun to enter a dark room with through a small aperture in a window and placed a glass prism in the path of white light .the light coming out of the prism was received on a white screen .on the screen a coloured patch like a rainbow was found which was termed as spectrum .starting from the side of the base of the prism the colours of the spectrum on the screen in the following order violet Indigo blue green yellow orange and red the order of colouring.

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Satyajeet Kumar

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