Dispersion of LightDispersion of Light

Projectee - Nishtha PathakProjectee - Nishtha Pathak

Class - 10Class - 10thth ‘B’ ‘B’

What is Dispersion?What is Dispersion?

The splitting up of white light into its seven constituent The splitting up of white light into its seven constituent

colours on passing through a transparent medium (like colours on passing through a transparent medium (like

glass prism) is called dispersion of light.glass prism) is called dispersion of light.

Cause of DispersionCause of Dispersion

The dispersion of white light occurs because colours of The dispersion of white light occurs because colours of white light travel at different speeds through the glass white light travel at different speeds through the glass prism. The amount of refraction depends on the speed prism. The amount of refraction depends on the speed of coloured light in glass. Now, since the different of coloured light in glass. Now, since the different colours travel at different speeds, they are refracted by colours travel at different speeds, they are refracted by different angles on passing through the glass prism. different angles on passing through the glass prism. So, when white light consisting of seven colours falls So, when white light consisting of seven colours falls on a glass prism, each colour in it is refracted by a on a glass prism, each colour in it is refracted by a different angle, with a the result that seven colours different angle, with a the result that seven colours spread out to form a spectrum. spread out to form a spectrum.

SpectrumSpectrum

The band of seven colours formed on a white screen, The band of seven colours formed on a white screen,

when a beam of white light is passed through a glass when a beam of white light is passed through a glass

prism, is called spectrum of white light. The seven prism, is called spectrum of white light. The seven

colours of the spectrum are: Violet, Indigo, Blue, colours of the spectrum are: Violet, Indigo, Blue,

Green, Yellow, Orange, and Red. It can be denoted by Green, Yellow, Orange, and Red. It can be denoted by

the word VIBGYOR.the word VIBGYOR.

Newton’s ExperimentNewton’s Experiment

Newton performed an experiment to show that white Newton performed an experiment to show that white

light consist of colours. A white light ray is passed light consist of colours. A white light ray is passed

through a prism to split it into the colours of the through a prism to split it into the colours of the

spectrum. The different coloured light is allowed to spectrum. The different coloured light is allowed to

pass through an identical prism kept in inverted pass through an identical prism kept in inverted

position. The light emerging out of second prism was position. The light emerging out of second prism was

found to be white indicating that the light ray consist of found to be white indicating that the light ray consist of

colours. colours.

RainbowRainbow

A rainbow is a natural spectrum appearing in the sky A rainbow is a natural spectrum appearing in the sky after a rain shower. It is caused by dispersion of after a rain shower. It is caused by dispersion of sunlight by tiny water droplets present in the sunlight by tiny water droplets present in the atmosphere. A rainbow is always formed in a direction atmosphere. A rainbow is always formed in a direction opposite to that of the Sun. The water droplets acts opposite to that of the Sun. The water droplets acts like a small prism. They refract and disperse the like a small prism. They refract and disperse the incident sunlight, then reflect it internally, and finally incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. Due refract it again when it comes out of the raindrop. Due to the dispersion of light and internal reflection, to the dispersion of light and internal reflection, different colours reach the observer’s eye.different colours reach the observer’s eye.

Lets Find Out More FactsLets Find Out More Facts

What is the range of visible light?What is the range of visible light?

Range of visible light – 0.4 microns to 0.7 microns.Range of visible light – 0.4 microns to 0.7 microns.

Visible light has a large number of radiations having Visible light has a large number of radiations having wavelengths ranging from 0.4 microns to 0.7 wavelengths ranging from 0.4 microns to 0.7 microns. That is, red light has a large wavelength microns. That is, red light has a large wavelength compared to violet light.compared to violet light.

Which component deviates Which component deviates maximum?maximum?

The violet colour has the minimum speed in prism, The violet colour has the minimum speed in prism, so the violet colour is deviated the maximum. so the violet colour is deviated the maximum.

Which component deviates Which component deviates minimum?minimum?

The red colour has the maximum speed in prism, so The red colour has the maximum speed in prism, so the red colour is deviated the minimum. the red colour is deviated the minimum.

Rate of photosynthesis?Rate of photosynthesis?

Wavelength of the component that increases the Wavelength of the component that increases the rate of photosynthesis - 0.7 microns.rate of photosynthesis - 0.7 microns.

The rate of photosynthesis is the most in the The rate of photosynthesis is the most in the presence of red light.presence of red light.

Which colour doesn’t affect the rate Which colour doesn’t affect the rate of photosynthesis?of photosynthesis?

Component which does not affect the rate of Component which does not affect the rate of photosynthesis - green light.photosynthesis - green light.

The rate of photosynthesis is zero in the presence of The rate of photosynthesis is zero in the presence of green light.green light.

What is the nature of the spectrum What is the nature of the spectrum emerging out of the first prism?emerging out of the first prism?

Nature of the spectrum emerging out of the first Nature of the spectrum emerging out of the first prism - a band or spectrum of seven colours is prism - a band or spectrum of seven colours is obtained.obtained.

The prism splits white light into seven colours.The prism splits white light into seven colours.

What is the nature of the spectrum What is the nature of the spectrum emerging out of the second prism?emerging out of the second prism?

Nature of the spectrum emerging out of the second Nature of the spectrum emerging out of the second prism – white light is obtained.prism – white light is obtained.

The seven colours of the visible spectrum combine The seven colours of the visible spectrum combine to form white light.to form white light.