Light is a form of energy. Vision is light bouncing back from various objects to one’s eyes. Our eyes are capable of seeing the white light coming from sun’s rays. It is actually a mixture of many colours. VIBGYOR is the term widely used to remember these colours. VIBGYOR stands for Violet, Indigo, Blue, Green, Yellow, Orange and Red.
You might have read about the standard experiment that proves that white ray is composed of different colors. This involves a ‘prism’ made of glass or plastic and is triangular in shape. Now glass is the medium through which light will pass through.
Every medium has a ‘refractive index’. It is nothing but a measure of bending of rays when it travels from one medium to another. This index can also be defined as the ratio of speed of light in vacuum to that in the given medium. Depending upon the refractive index, light bends at different angles in different medium. Dispersion of light occurs because of the refractive index.
A ray of light is made to fall on one side of prism. One must observe that the light now travels from one medium ‘air’ into another medium ‘glass’. As it travels it bends because of the refractive index of glass. Finally light has to travel from glass to air. In doing so they spread out like a rainbow.
In the sky, the raindrops in air molecules act as very small prisms. When sunlight passses through rain drops , rainbow gets formed. Light travels at different speeds in different mediums. Speed of light in vacuum is 186,000 miles per second (300,000 kilometers per second).
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