Q17 of 40 Page 1

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 an 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.

White light is a combination of 7 colours. Different colours light has different speed and different wavelength. Hence for each wavelength or colours of the light refractive index is different. So they bend at different angles when passes through a prism. Thus white light gets splits into its 7 constituent colours. This process is called dispersion.

Newton allowed passing a thin beam of white light on a prism which gets split into its constituent 7 colours. Then he allowed passing these 7 colours of light through an inverted prism as shown in below figure. Only a beam of white light comes out from the second prism thus he concluded that white light is made up of 7 colours.



More from this chapter

All 40 →
15

‘‘Evolution and classification of organisms are interlinked.’’ Give reasons to justify this statement.

 16

If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system?

 18

Water is an elixir of life, a very important natural resource. Your Science teacher wants you to prepare a plan for a formative assessment activity, ‘‘How to save water, the vital natural resource’’. Write any two ways that you will suggest to bring awareness in your neighbourhood, on ‘how to save water’.

 18

Name and explain any one way by which the underground water table does not go down further.