# Chapter Unit - 2 : Light[Dispersion through a Prism and Electromagnetic Spectrum] - Frank Solutions for Class 10 Physics ICSE

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## Chapter 2 - Light[Dispersion through a Prism and Electromagnetic Spectrum] Excercise 123

Question 1
What do you mean by dispersion?
Solution 1
The phenomenon of splitting of white light into its constituent colours is known as dispersion.
Question 2
Solution 2
Question 3
What is the velocity of electromagnetic wave?
Solution 3
3 x 108 m/s is the velocity of electromagnetic radiation.
Question 4
How does the deviation produced by a triangular prism depend on the colours (or wavelengths) of light incident on it? Which colour deviates the most and which the least?
Solution 4
Light of different colours have different speeds in a medium.
Therefore, the refractive index of glass (the material of prism) is different for different colours of light and the deviation caused by a prism is different for different colours of light.
Violet is deviated the most because in glass, speed of violet is least.
Red is deviated the least because in glass, speed of red is most.
Question 5
What do you understand by the term spectrum?
Solution 5
The colour band obtained on a screen on passing white light through a prism is called the spectrum.
Question 6
Solution 6
Question 7
(i) If a monochromatic beam of light undergoes minimum deviation through an equiangular prism, how does the beam pass through the prism, with respect to its base?
(ii) If white light is used in same way as in (i) above, what change is expected in the emergent beam?
Solution 7
(i) It passes parallel with respect to the base of the prism.
(ii) The white light shall split into its constituent colours and a spectrum shall be formed.
Question 8
Express nanometer (nm) in terms of Angstrom
Solution 8

## Chapter 2 - Light[Dispersion through a prism and electromagnetic spectrum] Excercise 124

Question 1
What do you mean by spectrum?
Solution 1
The colour band obtained on a screen on passing white light through a prism is called the spectrum.
Question 2
Will dispersion result when a monochromatic light passes through a prism?
Solution 2
If a monochromatic light passes through a prism, deviation will occur and not dispersion.
Question 3
What is the cause of dispersion?
Solution 3
Dispersion occurs because light of different colour bend through different angles while passing through a glass prism.
Question 4
Briefly, describe an experiment to show that a prism itself produces no colour.
Solution 4
Question 5
(i)    Draw a diagram to show the splitting of white light into its constituent colours.
(ii)    Draw another diagram to show how the colours of spectrum of white light can be combined to give the effect of white light.
Solution 5
Question 6
Complete the ray diagram given below to show the nature of light produced on the screen.
Solution 6
Question 7
Name the scientist who discovered
(i)    X-rays        (ii)    Visible light
(v)    Infra-red waves (vi)    Ultraviolet rays
Solution 7
(i) Roentgen
(ii) Newton
(iii) Hertz
(iv) Marconi
(v) Hershell
(vi) Ritter
Question 8
The wavelengths for the light of red and blue colours are roughly 7 X 10-7 m and 4 X 10-7 m respectively. Which colour has the greater speed in vacuum? Which colour has the greater speed in glass?
Solution 8
In vacuum both the colours have the same speed.
In glass, red colour has a greater speed.
Question 9
What is a spectrum? Draw a labeled ray diagram to show the formation of spectrum of white light.
Solution 9

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