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Sunlight - white and coloured - class-VIII

Description: sunlight - white and coloured
Number of Questions: 46
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Tags: spectra spectrum our colourful world option c: imaging wonders of visible light light human eye and colourful world physics light energy
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White light is a mixture of

  1. seven colors

  2. nine colors

  3. fifteen colors

  4. seventeen colors


Correct Option: A
Explanation:

White light is made up of seven colors namely Violet, Indigo, Blue, Green, Yellow, Orange, Red commonly remembered by using the acronym VIBGYOR. 

Hence, the correct answer is OPTION A.

Splitting of light into its constituent colours is known as :

  1. Reflection

  2. Refraction

  3. Diffraction

  4. Dispersion


Correct Option: D
Explanation:

When white light splits into different colors with different wavelengths then it is known as dispersion.

Clouds are white because of light scattering off of water droplets.

  1. True

  2. False


Correct Option: A
Explanation:

''Clouds are white because of light scattering off of water droplets''.  It is true as reflection is also scattering but in a defined way.

The splitting of white light into several colours on passing through a glass prism is due to -

  1. Refraction

  2. Reflection

  3. Interference

  4. None of these


Correct Option: A
Explanation:

The splitting of white light into its constituent colour is called dispersion. Dispersion occurs because refraction or bending differs with the colour.

What does the dispersion of light in a medium imply
i) Lights of different wavelength travel with different speeds in the medium.
ii) Light of any frequency will travel with the same speed in the medium
iii) The refractive index of the medium is different for different wavelength of light

  1. $(i)$ and $(ii)$ only

  2. $(ii)$ and $(iii)$ only

  3. $(i)$ and $(iii)$ only

  4. $(i),(ii)$ and $(iii)$


Correct Option: C

The colour are characterised by which of following character of light.

  1. Frequency

  2. Amplitude

  3. Wavelength

  4. Velocity


Correct Option: C
Explanation:

White light is incident combination of various colours each having different wavelengths. 

Thus colour is characterised by wavelength of light. 

The deflection of light by minute particles and molecules in all distraction is known as ____of light .

  1. dispersion

  2. interference

  3. diffraction

  4. scattering


Correct Option: A

When the white light is passed through a equilateral prism it splits into seven colours. The phenomena of splitting of white light is called :

  1. $refraction$

  2. $spectrum$

  3. $dispersion$

  4. $scattering$


Correct Option: C

The phenomenon due to which white light splits into seven colours on passing through a prism is called _________

  1. reflection

  2. refraction

  3. dispersion

  4. all the above


Correct Option: C
Explanation:

The phenomenon due to which white light splits into seven colours on passing through a prism is called dispersionWhite light is made up of seven bands of colors each having different wavelengths. Upon passing through a medium, each of the colors travels at different speeds and hence has different angles of refraction leading to the splitting of the light i.e. dispersion.

A rainbow is formed when the air is completely dry

  1. True

  2. False


Correct Option: B
Explanation:

False. It is formed only after or before the rains when the air is full of moisture

A ray of light after passing through a medium were spread up into different colours. The phenomenon is called :

  1. Total internal reflection

  2. Diffraction

  3. Dispersion

  4. Deviation


Correct Option: C
Explanation:

A ray of light after passing through a medium were spread up into different colours. The phenomenon is called dispersion.

Dispersion of white light into its constituent colours occurs during :

  1. Reflection at a plane mirror

  2. Reflection at a concave mirror

  3. Internal reflection inside a spherical drop of water

  4. Refraction at the boundary of a transparent medium


Correct Option: D
Explanation:

Answer is D.

The spectral colors of the rainbow are caused by dispersive refraction. Newton established that refraction causes the dispersion of light into its constituent colours. He named seven colors, in symmetry with the seven distinct notes in the Western musical scale.
Refraction is the bending of a light as it crosses the boundary into a different medium and it is determined by its refractive index, or how much the light is slowed down in the new medium.
Hence, dispersion of white light into its constituent colors occurs during refraction at the boundary of a transparent medium.

The splitting of white light into several colours on passing through a glass prism is due to

  1. refraction

  2. reflection

  3. dispersion

  4. none of these


Correct Option: C
Explanation:
$ \bf{Refraction} $ of light is the phenomenon of bending of light or change in the direction of light, when it passes obliquely from one transparent medium to another.

$ \bf{Reflection} $ is the phenomenon in which light rays on striking a polished surface(such as a mirror) bounce back or are sent back into the same medium. 

$\bf{Dispersion} $ is the phenomenon of splitting of white light into its component colours (VIBGYOR) on passing through a glass prism.


Hence, the correct answer is OPTION C.

The sky appears blue due to:

  1. reflection of light

  2. dispersion and scattering of light

  3. total internal reflection of light

  4. blue colour of water droplets


Correct Option: B
Explanation:

The sky appears blue due to dispersion and scattering of white light from the Sun and the blue color scatters the most because of its small wavelength as compared to other colors in spectrum.

The splitting of white light into its colored components is called _____.

  1. Spectrum

  2. Dispersion

  3. Deviation

  4. Refraction


Correct Option: B
Explanation:

The prism splits the incident light beam into a band of 7 colors. This band of colored components of a light beam is called its spectrum and the phenomenon of splitting of light into its component colours is called dispersion.

When white light passes through a dispersive medium, it breaks up into various colours. Which of the following is true?

  1. Velocity of light for violet is greater than the velocity of light for red colour

  2. Velocity of light for violet is less than the velocity of light for red

  3. Velocity of light is the same for all colours

  4. Velocity of light for different colours


Correct Option: B
Explanation:

When light falls on the glass prism, refraction takes place. Since the wavelength of different components of light is different and the frequency is constant, each component gets deviated by a different angle due to the difference in velocity in the glass medium. The red color having the maximum wavelength and velocity, deviates the least and forms the upper part of the spectrum whereas violet having the least wavelength and velocity deviates the most.

Which of the following are Primary pigments ?

  1. Yellow, green, magenta

  2. Magenta, yellow, cyan

  3. Blue, green, yellow

  4. Blue, green, violet


Correct Option: B
Explanation:

The primary colors of pigment are used when producing colors from reflected light; for example, when mixing paint or using a color printer. The primary colors of pigment are Magenta, Yellow, and Cyan. 

Hence, the correct answer is OPTION B.

Which of the following are Primary colors ?

  1. Red, blue, yellow

  2. Red, orange, yellow

  3. Red, blue, green

  4. Red, green, cyan


Correct Option: A
Explanation:
The primary colors are those which cannot be created by mixing other colors in a given color space. The primary colors are Red, Blue and Yellow.

Hence, the correct answer is OPTION A.

Why do we study the Dispersion phenomenon using a glass prism and not a glass slab ?

  1. Light doesn't undergo any deviation inside a glass slab; so cannot be used to study Disprsion

  2. All of the dispersion that takes place at the first interface is exactly reversed at the second parallel surface, 'undoing' the effect of the first interface.

  3. Dispersion occurs only in prism and not in glass slab

  4. None of the above


Correct Option: B
Explanation:
The Dispersion phenomenon using a glass prism and not a glass slab because when light passed through glass slab, it encounters TWO interfaces--one entering and the other leaving. All of the bending (and dispersion) that takes place at the first interfaces is exactly reversed at the second, 'undoing' the effect of the first interface; so although the emerging ray of light is displaced slightly from the entering ray, it travels in the same direction as the incoming ray and all wavelengths that separated at the first interface are re-combined. 
And in case of prism the second interface is NOT parallel to the first, the effects of the first interface are NOT reversed and the colors separated at that interface continue along different paths upon leaving the prism.

Dispersion of light is caused due to :

  1. intensity of light

  2. density of medium

  3. wavelength

  4. none of the above


Correct Option: C
Explanation:

The splitting of white light into its constituent colour is called dispersion of light. In this phenomenon, different colours contained in white emerge from the glass prism in different directions due to their different wavelengths.

A ray of light containing both red and blue colours is incident on the refracting surface of a prism. Then,

  1. both colours suffer equal deviation

  2. red colour suffers more deviation

  3. red colour suffers less deviation

  4. deviation depends on the angle of prism


Correct Option: C

The phenomenon of dispersion arises because of

  1. The decomposition of a white light beam by a prism

  2. The refraction of light

  3. The refractive index of the prism material being different for different wave length

  4. The corpuscular nature of light


Correct Option: C

Soap bubble appears coloured due to the phenomenon of:-

  1. Total internal feflection

  2. Interference by division of amplitude

  3. Interference by division of wavefront

  4. Diffraction of light


Correct Option: C
Explanation:
It is due to the interference of light. As the position of eyes is changed, path difference corresponding to different wavelength of the light emitted by the bubble change. Thus the intensities of different wavelengths are different resulting the bubble to be appeared colored. 
Option $-C$ is correct.

Oil floating on water looks coloured due to interference of light. What should be the order of magnitude of the thickness of oil layer in order that this effect may be observed?

  1. $10^{-6}\ m$

  2. $10^{-2}\ m$

  3. $10^{-10}\ m$

  4. $10^{-8}\ m$


Correct Option: A

Dispersion of ......... colour is minimum in visible range of light.

  1. Red

  2. Blue

  3. Green

  4. Violet


Correct Option: A

Calculate the angle of dispersion between red and violet colours produced by a flint glass prism of refracting angle of $60^0$. Given : $\mu _v = 1.663$ and $\mu _r = 1.622$.

  1. $4^0 6'$

  2. $5^0 6'$

  3. $3^0 4'$

  4. $6^0 4'$


Correct Option: A

Fill in the blanks:

The phenomenon of splitting of light into its component colours is ____________

  1. diffraction

  2. scattering

  3. dispersion

  4. refraction


Correct Option: C
Explanation:

Colours are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colours - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersion.

State whether the following statement is True or False. 

You can see a rainbow only when your back is towards the sun

  1. True

  2. False


Correct Option: A
Explanation:

A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky.

Now I won't get scientific, but apply your logic here.

Light which is reflected comes from the sun. So, rainbow is basically reflecting the light of the sun back. So think, how can you reflect something by staying at the same side as of the object you want to reflect?

When white light splits in seven colours, the phenomenon is called spectrum. 

  1. True

  2. False


Correct Option: B
Explanation:

The phenomenon of splitting of white light into seven constituent colors is known as dispersion.

                           And, the band of seven colours obtained on the screen is known as spectrum.

Given statement is $False$.

Dispersion of white light into its constituent colours occurs during 

  1. Reflection at a plane mirror

  2. Reflection at a concave mirror

  3. Internal reflection inside a spherical drop of water

  4. Refraction at the boundary of a transparent medium


Correct Option: D
Explanation:

Upon entry of white light at the first boundary of a triangular prism, there will be a slight separation of the white light into the component colours of the spectrum. Upon exiting the triangular prism at the second boundary, the separation becomes even greater and ROYGBIV is observed in its splendor. Hence, Dispersion of white light into its constituent colours occurs during refraction at the boundary of a transparent medium.

Dispersion of white light into its constituent colours occurs during

  1. reflection at a plane mirror

  2. reflection at a concave mirror.

  3. internal reflection inside a spherical drop of water

  4. refraction at the boundary of a transparent medium.


Correct Option: D
Explanation:

Upon entry of white light at the first boundary of a triangular prism, there will be a slight separation of the white light into the component colours of the spectrum. Upon exiting the triangular prism at the second boundary, the separation becomes even greater and ROYGBIV is observed in its splendor. Hence, Dispersion of white light into its constituent colours occurs during refraction at the boundary of a transparent medium.

Line spectrum is obtained from the :

  1. Sun

  2. Filament of the bulb

  3. Mercury lamp

  4. Burning coal


Correct Option: C
Explanation:

As a light source, we will use a mercury lamp, which emits light at several discrete wavelengths. The device we are using is called a prism spectrometer because, once the prism is calibrated, it can be used to measure the wavelengths of the lines in the spectra produced by various atoms.

A piece of cloth looks red in sun light. If it is held in the blue portion of a solar spectrum, it will appear

  1. Red

  2. Black

  3. Blue

  4. White


Correct Option: B
Explanation:

A cloth piece looks red in sun light because it absorbs all the colours of sun light except red, red is reflected to our eyes.

When red cloth piece is held in only the  blue portion of solar spectrum, the blue light will be absorbed by red cloth and as there is no red light is to reflect, therefore no colour will be reflected back i.e. cloth piece will appear black.

Which of the following colours of light undergoes the least deviation while passing through a glass prism ?

  1. Red

  2. Blue

  3. Yellow

  4. Green


Correct Option: A
Explanation:

Red goes through least deviation because it has highest speed among VIBGYOR.

We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
.

   so refractive index will be very less for red color and hence show least deviation.


The light which refracts most while passing through a prism is

  1. Red

  2. Violet

  3. Indigo

  4. Yellow


Correct Option: B
Explanation:

Violet is having shortest wavelength among VIBGYOR. 

We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
  so, refractive index property for violet will be maximum and it will refract the most.

Which of the following colour of light undergoes the maximum deviation while passing a glass prism ?

  1. Red

  2. Blue

  3. Violet

  4. Green


Correct Option: C
Explanation:

Violet undergoes maximum deviation while passing through a prism because it has least wavelength , as we know,

            We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
  so, refractive index property for violet will be maximum and it will refract the most. and will have the greatest deviation.

When light passes through a medium that consists of scatters such as water vapour, dust particles, which colour of light experiences highest scattering?

  1. $Violet$

  2. $Red$

  3. $Yellow$

  4. $Orange$


Correct Option: A
Explanation:

Violet have least wavelength among the visible light spectra.

       According to Rayleigh Criterion,  Scattering probability is proportional to $\dfrac{1}{\lambda^4}$.
So, violet light will be scattered the most.

When light enters a dispersive medium, light wave of different wavelength travels with different velocities.

  1. Yes

  2. No

  3. Sometimes

  4. When medium is a fibre


Correct Option: A
Explanation:

Yes, speed becomes different for different wavelengths in a particular medium. In a given dispersive medium the speed for different colours is different and due to this phenomenon we can see the spectrum of VIBGYOR.

Assertion: Different colours travel with different speed in vacuum.
Reason : Wavelength of light depends on refractive index of medium.

  1. Both assertion and reason are true but the reason is the correct explanation of assertion

  2. Both assertion and reason are true but the reason is not the correct explanation of assertion

  3. Assertion is true but reason is false

  4. Both the assertion and reason are false

  5. Reason is true but assertion is false


Correct Option: E
Explanation:

In vacuum all the colours have same velocity but their velocity changes when they enter in a medium. In the medium their velocity changes due to change in their wavelength.
$v=n\lambda $
If $\lambda $ changes, v also changes for a particular colour therefore, different colours have different wavelength ($\lambda $).

What is known as dispersion of light?

  1. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a transparent medium

  2. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a opaque medium

  3. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a translucent medium

  4. The phenomenon due to which a polychromatic light, like sunlight, do not splits into its component colours, when passed through a transparent medium


Correct Option: A
Explanation:

When white light pass through a glass prism the white light get scatter in so many colours of light according to it's frequency and the lights are (VIBGYOR) ,this phenomena of scattering of light is called
dispersion of light.

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Due to which property of colours they appear differently though the sunlight is passed through only one medium?

  1. Due to different refractive index with respect to medium

  2. Due to different frequencies with respect to medium

  3. Due to different amplitudes with respect to medium

  4. Due to different colour with respect to medium


Correct Option: A
Explanation:

Refraction is a phenomenon that happens when a beam of white light passes through the interface between air and a denser medium, such as glass or water. Light travels more slowly in a denser medium, so it changes direction – or refracts – when it passes through the interface. White light is a mixture of all the wavelengths of light, and each wavelength refracts at a slightly different angle. Therefore, when the beam emerges from the denser medium, it has been split into its component wavelengths. The ones you can see form the familiar rainbow

In the spectrum of white light which color is deviated minimum ?

  1. Red

  2. Yellow

  3. Violet

  4. Blue


Correct Option: A
Explanation:

Red colour having minimum refractive index and hence undergoes minimum deviation.


Answer-(A)

In spectrum obtained with prism which color is deviated maximum ?

  1. Violet

  2. Red

  3. Green

  4. Orange


Correct Option: A
Explanation:

Violet colour having higher refractive index and hence undergoes maximum deviation.


Answer-(A)

Which of the following scientists did the pioneering work to understand the splitting of white light in different components ?

  1. Thomas Edison

  2. Albert Einstein

  3. Issac Newton

  4. Archimedes


Correct Option: C
Explanation:

Newton was the first to understand that white light consists of a mix of light rays, each with a different colour.

The spreading of white light into its component colours is known as.

  1. Dispersion

  2. Deviation

  3. Refraction

  4. Diffraction


Correct Option: A
Explanation:

$\text{Defination of Dispersion :-}$

Dispersion is the phenomenon of spreading of white light into its component colors. 

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