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Dispersion

Introduction

     It is a matter of common experience that precious stones like diamonds, rubies, etc. or glass pieces glitter when light, particularly white light is incident on it. In this chapter let us find out why white light incident on a transparent prism splits into different colors.

Newton's Experiment - Dispersion of Light

     Sir Isaac Newton, while studying the images of heavenly bodies formed by a lens, found that the image is colored at its edges. In 1665, to investigate this, he performed an experiment using a prism.

Dispersion of White Light By a Glass Prism

     Even though all colors of the visible spectrum travel with the same speed in vacuum, the speed of the colors of the visible spectrum varies when they pass through a transparent medium like glass and water. That is, the refractive index of glass is different for different colors.

Recomposition of White Light

     Recombination of the seven colors of the dispersed white light to get white light is known as Recomposition of white light.

Color

     Color may be defined as the visual sensation which depends upon the wavelength or frequency of the light that enters the eye.

Complementary Colors

     A pair of colors which on mixing produce white are called complementary colors.

Color of Opaque Objects

     The color of a non-luminous, opaque object depends upon the color of the light reflected by it. The color of the reflected light depends upon the color of the incident light.

Color of Transparent Objects

     Any object which allows light to pass through it is known as a transparent object. The color of any transparent object is the color of the light transmitted by it.

How do We See Colors?

     The retina of our eye is composed of light sensitive cells. Light sensitive cells are of two types namely, rods and cones. There are three types of cones., those that are stimulated by low frequencies, those stimulated by intermediate frequencies and those stimulated by higher frequency visible light.

Color Deficiency or Color Blindness

     Color deficiency is that defect of the eye due to which a person is not able to distinguish between certain colors mainly due to the malfunctioning or absence of a particular cone.

Color Perception in Animals and Birds

     The structure and the number of rod shaped and cone shaped cells are different for animals and birds. For e.g., bees have cones sensitive to ultraviolet rays.

Summary

     Is the visual sensation which depends upon the wavelength or frequency of light that enters the eye.



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