Dispersion of light

1. Dispersion of LightDispersion of Light
Projectee - Nishtha PathakProjectee - Nishtha Pathak
Class - 10Class - 10
thth
‘B’ ‘B’

2. 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.

3. 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.

4. 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.

5. 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.

7. 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.

10. Lets Find Out More FactsLets Find Out More Facts

11. 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.

12. 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.

14. 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.

16. 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.

18. 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.

20. 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.

22. 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.