NCERT Exemplar Solutions Class 10 Science Human Eye and Colourful World

Multiple Choice Questions...........................

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 

Solution 1: (b) – 0.5 D 

Since the individual is myopic and requires a concave mirror, the power is negative.

P =  1/f =1/2 m = 0.5 D

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 textbook. 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 

Solution 2: (a) The near point of his eyes has receded away 

In hypermetropia, the near point of the eye moves 25 cm further. To read properly, the individual should hold the book 25 cm apart.

Question 3:  A prism ABC (with BC as a base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in the given 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) 

Solution 3: (b) (ii) 

If the prism is held with BC in the bottom, a violet band appears at the bottom. Violet would be at the tip of the prism if BC is at the top, followed by indigo and blue.

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 

Solution 4:  (b) all the colours of the white light are scattered away

At noon the sun appears white as, this is due to light scattering in the atmosphere.

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 

Solution 5: (c) Refraction, dispersion and internal reflection

Internal reflection is caused by the scattering of white light into various colours at an angle caused by light dispersion. The incident light is bent by refraction, resulting in the formation of a rainbow.

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 

Solution 6:  (b) refraction of light by different layers of varying refractive indices 

The direction of the source of light does not change due to refraction. The stars will twinkle as a result of this.

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 

Solution 7: (c) violet and blue lights get scattered more than lights of all other colours by the atmosphere. 

Since violet and blue lights are dispersed more than all other colours by the atmosphere, the clear sky looks blue. 

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 

Solution 8:  (c) All the colours of the white light move with the same speed

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  

Solution 9:  (b) is scattered the least by smoke or fog 

The wavelength of red is the longest, so it can be seen from a long distance. It's the colour that's least affected by smoke or smog. 

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 

Solution 10:   (b) Scattering of light 

Since red scatters the least, it flies the furthest. Light must travel a long way to reach the earth at sunset or sunrise. As a result, when light hits us, it will be red. 

Question 11:  The bluish colour of water in the 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 

Solution 11:  (b) reflection of sky in water 

Water is colourless, but it takes on the colour of the reflected light. As a result, the sea looks blue. 

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   

Solution 12: (b) the outer surface of the cornea 

The cornea is a thin membrane that allows light to pass through. Since the incident light rays are bent and converged by the cornea, an image is formed at the retina. As a result, the iris of the eye is where the majority of the refraction occurs. 

Question 13:  The focal length of the eye lens increases when eye muscles 

(a) are relaxed and the lens becomes thinner 

(b) contract and lens becomes thicker 

(c) are relaxed and the lens becomes thicker 

(d) contract and lens becomes thinner

 Solution 13:  (a) are relaxed and the lens becomes thinner 

When the eye muscles relax and the lens thins, the focal length of the lens increases. 

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 

Solution 14:  (c) A person with myopia can see nearby objects clearly  

Myopia is a disorder in which a person can see nearer objects clearly but cannot see distant objects clearly. 

Hypermetropia is a disorder in which a person cannot see clearly close objects but can see clearly far away objects. 

Short Answer Questions............................

Question 15: Draw ray diagrams each showing

(i) myopic eye and

(ii) hypermetropic eye. 

Solution 15:

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. 

Solution 16:  Myopia is a condition in which a student cannot see the blackboard when it is far away from her. As a result, the doctor recommends a concave lens with a suitable focal length.

Question 17:  How are we able to see nearby and also the distant objects clearly? 

Solution 17:  By adjusting the focal length of the lens, our eyes will focus on images from a variety of distances. Ciliary muscle action aids in changing the focal length of the lens.

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? 

Solution 18:  (a) Myopia is the defect in vision she is suffering from.