April 10, 2026
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Chapter 11: The Human Eye and the Colourful World
Complete NCERT Solutions (Intext + Exercise) | CBSE Class 10 Science | Questions & Marks
Class 10- Science Solutions
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Class 10 (CBSE) - SYLLABUS
Class 10 (CBSE) - PYQ
Intext Questions (Page 190)
12 marks
What is meant by power of accommodation of the eye?
Answer: Power of accommodation is the ability of the eye lens to adjust its focal length to see objects at different distances clearly.
22 marks
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Answer: Concave lens (diverging lens) of appropriate focal length.
32 marks
What is the far point and near point of the human eye with normal vision?
Answer: Far point – infinity; near point – 25 cm.
42 marks
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Answer: Myopia (short-sightedness). Corrected by using concave lens of appropriate power.
Intext Questions (Page 197)
52 marks
The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to (a) presbyopia (b) accommodation (c) near-sightedness (d) far-sightedness.
Answer: (b) accommodation.
62 marks
The human eye forms the image of an object at its (a) cornea (b) iris (c) pupil (d) retina.
Answer: (d) retina.
72 marks
The least distance of distinct vision for a young adult with normal vision is about (a) 25 m (b) 2.5 cm (c) 25 cm (d) 2.5 m.
Answer: (c) 25 cm.
82 marks
The change in focal length of an eye lens is caused by the action of the (a) pupil (b) retina (c) ciliary muscles (d) iris.
Answer: (c) ciliary muscles.
NCERT Exercise Questions (Page 198)
Ex 12 marks
What is meant by the dispersion of white light? Describe the formation of rainbow in the sky with the help of a diagram.
Answer: Dispersion is splitting of white light into its constituent colours. Rainbow forms due to dispersion and total internal reflection of sunlight in water droplets.
Ex 22 marks
What is the difference between a glass slab and a glass prism?
Answer: Glass slab has parallel faces – emergent ray is parallel to incident ray. Glass prism has non-parallel faces – emergent ray is deviated and dispersed.
Ex 32 marks
A star appears slightly higher than its actual position in the sky. Explain why.
Answer: Due to atmospheric refraction, light from the star bends towards normal as it enters denser layers, making the star appear higher than its actual position.
Ex 42 marks
Why do we see a rainbow in the sky only after rainfall?
Answer: After rainfall, water droplets remain suspended in air. Sunlight enters these droplets, undergoes dispersion and internal reflection, forming a rainbow.
Ex 52 marks
Why is the colour of the sky blue?
Answer: Blue light scatters more than other colours due to Rayleigh scattering by atmospheric particles. The scattered blue light reaches our eyes from all directions.
Ex 63 marks
A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
Answer: (i) P = -5.5 D, f = 1/P = -0.1818 m = -18.18 cm. (ii) P = +1.5 D, f = 1/1.5 = 0.6667 m = 66.67 cm.
Ex 72 marks
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Answer: Myopia corrected by concave lens. For distant object (u = ∞), image at far point (v = -80 cm). 1/f = 1/v - 1/u = -1/0.8 - 0 = -1.25 D. Power = -1.25 D.
Ex 83 marks
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Answer: Hypermetropia corrected by convex lens. u = -25 cm, v = -1 m = -100 cm. 1/f = 1/v - 1/u = -1/100 - (-1/25) = -0.01 + 0.04 = 0.03 => f = 33.33 cm = 0.3333 m, P = 1/f = +3.0 D.
Ex 92 marks
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Answer: The ciliary muscles cannot contract further beyond a point, and the eye lens cannot increase its curvature enough to focus objects closer than 25 cm.
Ex 102 marks
What happens to the image distance in the eye when we increase the distance of an object from the eye?
Answer: The image distance remains fixed (distance between lens and retina). The focal length changes to focus the image on the retina.
Ex 112 marks
Why do stars twinkle?
Answer: Atmospheric refraction causes starlight to bend continuously as it passes through layers of varying refractive indices. This makes the star appear to twinkle.
Ex 122 marks
Explain why the planets do not twinkle.
Answer: Planets are closer and appear as tiny discs, not point sources. Light from different points cancels out twinkling effects.
Ex 132 marks
Why is the sky blue? What would the colour of the sky be on a planet with no atmosphere?
Answer: Blue due to Rayleigh scattering. On a planet with no atmosphere, the sky would appear black.
Additional Important Questions
A12 marks
What is presbyopia? How is it corrected?
Answer: Age-related defect where both near and far vision become poor. Corrected by bifocal lenses (convex + concave).
A22 marks
What is Tyndall effect? Give an example.
Answer: Scattering of light by colloidal particles. Example: blue colour of sky due to scattering by air molecules.
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