# . State the cause of dispersion of white light passing through a glass prism. How did Newton

show  that white  light  of Sun  contains seven  colours  using  two identical glass prisms

Ans. i.  White light is a mixture of lights .of seven colours, red, orange, yellow, green, blue, indigo and violet. The dispersion of white light occurs because colours of white light travel at different speeds through the glass prism. The amount of refraction depends on the speed of coloured light in glass.

ii. When white light consisting of seven colours falls on a glass prism, each colour in it is refracted by a different angle, with the result that seven colours are spread out  to form a spectrum.  The red light bends the least, while violet bends the most. Newton's experiment with two identical prisms:

iii. When a beam of white light is passed through a glass prism, a band of seven colours is formed on a white screen. This band of seven colours is called spectrum of white light.

iv.  Newton showed  that the seven coloured lights of the spectrum can be recombined  to give back white light.

v. First he tried to split the colours of the spectrum of white light using a prism.

vi. He then placed a second identical prism in an inverted position with respect to the first prism. This allowed all the colours of the spectrum to pass through the second prism. Hfound  a beam of white light emerging  from the other side of the second prism.