Science Ncert Exemplar Solutions for Class 10 Science Chapter 11 The Human Eye And The Colourful World are provided here with simple step-by-step explanations. These solutions for The Human Eye And The Colourful World are extremely popular among Class 10 students for Science The Human Eye And The Colourful World Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science Ncert Exemplar Book of Class 10 Science Chapter 11 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science Ncert Exemplar Solutions. All Science Ncert Exemplar Solutions for class Class 10 Science are prepared by experts and are 100% accurate.

Page No 86:

Question 1:

A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
(a) +0.5 D
(b) –0.5 D
(c) +0.2 D
(d) –0.2 D

Answer:


The person is suffering from myopia. He needs a concave lens and hence power would be negative.
P=1f= 12m= 0.5D

Hence, the correct answer is option A.

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Question 2:

A student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his text book. Which of the following statements is correct?
(a) The near point of his eyes has receded away
(b) The near point of his eyes has come closer to him
(c) The far point of his eyes has come closer to him
(d) The far point of his eyes has receded away

Answer:

The near point of his eye has receded away.
In hypermetropia, the near point of the eye moves away from 25cm. Due to this, the person needs to keep the book at more than 25cm to read it properly.

Hence, the correct answer is option A.

Page No 86:

Question 3:

A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in Figure . In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky?

(a) (i)
(b) (ii)
(c) (iii)
(d) (iv)

Answer:


If Prism is kept with base BC at the bottom, then the emerged band of colour would show violet at the bottom. 
If Prism is kept with base BC at the top, then violet would be at the top, followed by indigo and blue


Hence, the correct answer is option  C.



Page No 87:

Question 4:

At noon the sun appears white as
(a) light is least scattered
(b) all the colours of the white light are scattered away
(c) blue colour is scattered the most
(d) red colour is scattered the most

Answer:


Sky will appear dark in case of option (a). It will appear blue in case of option (c) and will appear red in case of option (d).
Hence,  all the colours of the white light are scattered away in noon so the sky appears white.

Hence, the correct answer is option  A.

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Question 5:

Which of the following phenomena of light are involved in the formation of a rainbow?
(a) Reflection, refraction and dispersion
(b) Refraction, dispersion and total internal reflection
(c) Refraction, dispersion and internal reflection
(d) Dispersion, scattering and total internal reflection
 

Answer:

Dispersion results in white light segregating into its 7 constituent colours. Refraction bends the incident light to an angle that it causes total internal reflection, and finally rainbow is formed.

Hence, the correct answer is option  B.

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Question 6:

Twinkling of stars is due to atmospheric
(a) dispersion of light by water droplets
(b) refraction of light by different layers of varying refractive indices
(c) scattering of light by dust particles
(d) internal reflection of light by clouds

Answer:


Due to the refraction of light by different layers of varying refractive indices, the apparent position of the source of light keeps on changing.
Due to this, start appears to twinkle.

Hence, the correct answer is option  B.

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Question 7:

The clear sky appears blue because
(a) blue light gets absorbed in the atmosphere
(b) ultraviolet radiations are absorbed in the atmosphere
(c) violet and blue lights get scattered more than lights of all other colours by the atmosphere
(d) light of all other colours is scattered more than the violet and blue colour lights by the atmosphere

Answer:

Violet and blue light get scattered more than lights of all other colours by the atmosphere.

Hence, the correct answer is option C.

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Question 8:

Which of the following statements is correct regarding the propagation of light of different colours of white light in air?
(a) Red light moves fastest
(b) Blue light moves faster than green light
(c) All the colours of the white light move with the same speed
(d) Yellow light moves with the mean speed as that of the red and the violet light

Answer:

 All the colours of white light move at the same speed.

Hence, the correct answer is option  C.

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Question 9:

The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light
(a) is scattered the most by smoke or fog
(b) is scattered the least by smoke or fog
(c) is absorbed the most by smoke or fog
(d) moves fastest in air

Answer:

The red light is scattered the least by smoke or fog and hence it is visible clearly from large distances.

Hence, the correct answer is option B.



Page No 88:

Question 10:

Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light from the earth
 

Answer:

Red colour scatters the least and hence travels the farthest. During sunset or sunrise, light has to travel a longer distance to reach us. 
Hence, only red light reaches us and the sky appears reddish.

Hence, the correct answer is option B.

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Question 11:

The bluish colour of water in deep sea is due to
(a) the presence of algae and other plants found in water
(b) reflection of sky in water
(c) scattering of light
(d) absorption of light by the sea
 
 

Answer:

The ocean looks blue because water is transparent i.e. colourless and so it reflects the colour of sky (which is blue because - red, orange and yellow (long-wavelength light) are absorbed more strongly by atmosphere/sky than by blue (short-wavelength light))

Hence, the correct answer is option B.

Page No 88:

Question 12:

When light rays enter the eye, most of the refraction occurs at the
(a) crystalline lens
(b) outer surface of the cornea
(c) iris
(d) pupil
 
 

Answer:

When the light rays enter the eye through a thin membrane, it enters through the transparent bulge on the front surface of the eyeball, called the cornea. Most of the refraction for the light rays entering the eye occurs at this outer surface of the cornea.

Hence, the correct option is B.

Page No 88:

Question 13:

The focal length of the eye lens increases when eye muscles
(a) are relaxed and lens becomes thinner
(b) contract and lens becomes thicker
(c) are relaxed and lens becomes thicker
(d) contract and lens becomes thinner
 
 

Answer:

The focal length of the eye lens increases when the eye muscles are relaxed and becomes thinner.

Hence, the correct answer is option A.

Page No 88:

Question 14:

Which of the following statement is correct?
(a) A person with myopia can see distant objects clearly
(b) A person with hypermetropia can see nearby objects clearly
(c) A person with myopia can see nearby objects clearly
(d) A person with hypermetropia cannot see distant objects clearly
 

Answer:

Nearsightedness or myopia is the inability of the eye to see the far located objects clearly.

Hence, the correct option is C.

Page No 88:

Question 15:

Draw ray diagrams each showing (i) myopic eye and (ii) hypermetropic eye.
 
 
 

Answer:

(i) Myopic eye: myopia is caused by elongation of the eyeball which results in focusing on the image in front of the retina. Thus, the distant images are blurry but the nearby images are clear.

(ii) Hypermetropic eye: Loss of flexibility is characterized by focusing on the image behind the retina. In this case, distant images are clear but the nearby images are blurry and the condition is termed as hypermetropia.

Page No 88:

Question 16:

A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.
 

Answer:

The student is having myopia which is caused by elongation of eyeball resulting in focusing of the image in front of the retina. Thus, the distant images are blurry but the nearby images are clear.


Wearing of concave lens diverges the light rays to help the image to be focused on the retina; myopia is corrected using the concave lens.

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Question 17:

How are we able to see nearby and also the distant objects clearly?
 

Answer:

Eyes have the ability to adjust its focal length which is known as the power of accommodation and we can see nearby and also the distant objects clearly. Relaxation of muscles makes the lens thinner and its focal length increases to make us see the distant objects clearly. The contraction of ciliary muscles increases the curvature of the eye lens and makes the eye lens thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.



Page No 89:

Question 18:

A person needs a lens of power –4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?
 

Answer:

(a) The negative power of the lens suggests that she must be suffering from myopia.

(b) Power, P = ─4.5 D, focal length, f = ?

Now,    P = 1/ f

⟹       f = 1/ P = 1/ −4.5 = −0.222m = − 22.2 cm

(c) Myopia is corrected using a concave or divergent lens.

Page No 89:

Question 19:

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Answer:

When the second identical prism placed in an inverted position with respect to the first prism, the condition is fulfilled.

Page No 89:

Question 20:

Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
 
 
 
 

Answer:

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Question 21:

Is the position of a star as seen by us its true position? Justify your answer.

Answer:

No, the light of stars enters the earth’s atmosphere and undergoes refraction continuously before reaching the earth. The atmospheric refraction takes place under a gradually changing refractive index. Since, starlight bends towards the normal; star appears slightly higher than the actual position.

Page No 89:

Question 22:

Why do we see a rainbow in the sky only after rainfall?

Answer:

Raindrops present in the atmosphere after rainfall serve as a prism and refract, disperse and internally reflect the incident sunlight followed by final refraction. The whole sequence of dispersion and internal reflection leads to the formation of the rainbow after rainfall in the sky.

Page No 89:

Question 23:

Why is the colour of the clear sky blue?

Answer:

It is caused by Rayleigh scattering of sunlight. The molecules in the air scatter blue light more than red light as blue light has shortest wavelength as compared to that of red light which has about 1.8 times greater than blue light.

Page No 89:

Question 24:

What is the difference in colours of the Sun observed during sunrise/sunset and noon? Give explanation for each.

Answer:

During sunrise/sunset, the sun looks reddish because, at this stage, Sunrays travel longer distance in the atmosphere and the red light having the largest wavelength is scattered the least. During noon, the sun is directly overhead and sunlight travels relatively shorter distance causing only little of the blue and violet colors to be scattered.

Page No 89:

Question 25:

Explain the structure and functioning of Human eye. How are we able to see nearby as well as distant objects?

Answer:

Structure of the human eye: Cornea is the transparent window of the eye that serves in the refraction of most of the light rays entering the retina. Iris is the coloured part of the eye that controls the amount of light by regulating the pupil size. The pupil is a hole shaped opening in the middle of the eye. The retina is the innermost layer of the eye and contains an outer pigmented layer and an inner nervous layer. It has photoreceptors (rods and cones). The optic nerve consists of nerve fibres from the innermost layer of the retina and serves to transmit the impulse to the brain. The eye lens is made up of fibrous, jelly-like material and transparent structure. It serves to form an inverted real image of the object on the retina. Vitreous humour is clear, a semi-solid structure that supports the eyeball.


Functioning of the human eye:  Light enters the eye through the pupil and then the eye lens converges these light rays on the retina. An inverted real image of the object is formed on the retina and image-electric signals are to the brain via the optic nerves. The brain reconstructs the erect image of objects and we can see the objects.

We are able to see nearby as well as distant objects due to the eye’s ability to adjust its focal length which is known as the power of accommodation. Relaxation of muscles makes the lens thinner and its focal length increases to make us see the distant objects clearly. Contraction of ciliary muscles increases the curvature of the eye lens and makes the eye lens thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.

 

Page No 89:

Question 26:

When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?
 

Answer:

Myopia: This eye defect is caused by elongation of the eyeball which results in focusing on the image in front of the retina. This causes the formation of blurry images of the distant images but the nearby images are clear.


Correction of Myopia: Wearing of concave lens diverges the light rays to help the image to be focused on the retina, hence myopia is corrected using the concave lens.


Hypermetropia: Loss of flexibility or too short eyeball causes focusing of the image behind the retina. In both cases, distant images are clear but the nearby images are blurry and the condition is termed as hypermetropia.


Correction of hypermetropia: Wearing a convex lens (plus powered) in front of a hypermetropic eye moves the image forward and focuses it correctly on the retina.


 

Page No 89:

Question 27:

Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Hence define the angle of deviation.

Answer:

The light ray PE enters from air to glass (rarer to denser medium) at surface AB and therefore, bends towards the normal. The refracted ray EF now exits from glass and enters air (from denser to rarer medium) and therefore, bends away from the normal. Extrapolation of the incident and emergent ray gives the angle of deviation.

Page No 89:

Question 28:

How can we explain the reddish appearance of sun at sunrise or sunset? Why does it not appear red at noon?
 

Answer:

It is caused by Rayleigh scattering of sunlight. The molecules in the air scatter blue light more than red light as blue light has the shortest wavelength as compared to that of red light which has about 1.8 times greater than blue light. The sky appears blue. During sunrise/sunset, the sun looks reddish because, at this stage, Sunrays travel longer distances in atmosphere and blue and green light (having shortest wavelength) of the visible spectrum is scattered away fully while the red light having the largest wavelength is scattered the least.



Sun is directly overhead and sunlight travels relatively shorter distance causing only little of the blue and violet colors to be scattered.

Page No 89:

Question 29:

Explain the phenomenon of dispersion of white light through a glass prism, using suitable ray diagram.
 

Answer:

Splitting of light into its constituent colors is referred to as dispersion. When a narrow beam of white light falls on a triangular glass prism, the light of different colors have different refractive indices in the glass. However, the speed of light is the same irrespective of its colors. Different refractive indices of different colors of light lead to their different bending pattern. This causes splitting of white light into light of seven colors called as VIBGYOR. V= violet, I= indigo, B=blue, G=green, Y= yellow, O=orange, R=red.


The light of red color bends the least on passing through the prism and appears at the top while violet color bends through the maximum angle and appears at the bottom.

Page No 89:

Question 30:

How does refraction take place in the atmosphere? Why do stars twinkle but not the planets?

Answer:

Optical densities of air particles change with changing height. This, in turn, produces a different pattern of refraction of light by the earth's atmosphere. The continuously changing physical conditions air produce different patterns of refraction of light stars. The greater the refraction is, the brighter the star look. The lesser the refraction is, the dimmer the star look. This different refraction pattern through different air layers makes stars look twinkling.

The planets are present much closer to the earth as compared to stars which make planets look like an extended source of light, not like a point-sized source of light as stars appear. This results in an average of least and maximum refraction as zero making the planets to look stationary, not twinkling like stars.



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