CBSE Class 10 Science NCERT Solutions: Human Eye and Colourful World

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NCERT Solutions PDF Class 10 PDF

This chapter delves into the fascinating workings of the human eye and common vision defects. The NCERT Solutions for Class 10 Science, Chapter 11: Human Eye and Colourful World, provide detailed explanations for key concepts. Students will learn about the eye's ability to adjust its focus, known as the power of accommodation, and understand why certain individuals struggle to see distant or near objects clearly. The solutions cover common refractive errors like myopia (nearsightedness) and hypermetropia (farsightedness), explaining their causes and how they can be corrected using lenses. This resource is designed to help students grasp the fundamental principles of optics as applied to the human eye, aiding in their exam preparation and understanding of visual perception.

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Quick info

BoardCBSE
ClassClass 10
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 11: Human Eye and Colourful World

Chapter summary

Chapter 11 of the NCERT Class 10 Science textbook focuses on the Human Eye and the Colourful World. These solutions explain the eye's mechanism of accommodation, enabling it to focus on objects at varying distances. They also address common vision defects such as myopia and hypermetropia, detailing the reasons behind them and the corrective measures, primarily the use of concave and convex lenses, respectively. The exercises cover understanding these concepts and applying them to practical scenarios.

Learning outcomes

  • Understand the concept of the power of accommodation in the human eye.
  • Identify and explain the defect of myopia and its correction.
  • Determine the far point and near point of a normal human eye.
  • Analyze vision problems like difficulty seeing distant objects and suggest corrective lenses.

Topics covered

Paper topics

  • Human Eye
  • Power of Accommodation
  • Ciliary Muscles
  • Eye Lens
  • Focal Length
  • Myopia (Nearsightedness)
  • Far Point
  • Near Point
  • Corrective Lenses
  • Concave Lens

Important topics

  • Power of Accommodation
  • Myopia: Cause and Correction
  • Near Point and Far Point of Normal Eye
  • Role of Concave Lens in Correcting Myopia

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Questions and Solutions

Question 1

What is meant by the power of accommodation of the eye?
Solution: The ability of the human eye to adjust its focal length to focus on objects at different distances is called the power of accommodation. When we look at distant objects, the ciliary muscles relax, causing the eye lens to become thinner and increasing its focal length. This allows us to see distant objects clearly. Conversely, when we look at nearby objects, the ciliary muscles contract, making the eye lens thicker and decreasing its focal length. This adjustment enables us to see nearby objects distinctly. Thus, the eye can adjust its focal length to form a clear image on the retina for objects located at various distances.

Question 2

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?
Solution: The defect described is myopia (nearsightedness), where the person can see nearby objects clearly but struggles to see distant objects. This happens because the eye's lens focuses the image of distant objects in front of the retina, rather than directly on it. To correct this, a lens is needed that will diverge the light rays slightly before they enter the eye, effectively shifting the focal point back onto the retina. A concave lens is used for this purpose. By placing a concave lens of appropriate focal length in front of the eye, the light rays from distant objects are diverged, and the eye lens then converges them to form a sharp image on the retina. Therefore, a concave lens should be used to correct this vision defect.

Question 3

What is the far point and near point of the human eye with normal vision?
Solution: For a human eye with normal vision:

The near point is the minimum distance at which an object can be seen distinctly without any strain. For a normal eye, this distance is approximately 25 cm.

The far point is the maximum distance at which an object can be seen clearly by the eye. For a normal human eye, the far point is considered to be at infinity.

Question 4

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?
Solution: The student's difficulty in reading the blackboard while sitting in the last row indicates that they are unable to see distant objects clearly. This vision defect is known as myopia (or nearsightedness). In myopia, the eye focuses images of distant objects in front of the retina instead of on it. This defect can be corrected by using a concave lens. A concave lens diverges the incoming light rays from the distant object before they reach the eye's lens. This divergence allows the eye's lens to focus the image correctly on the retina, enabling the student to see the blackboard clearly.

Common mistakes

  • Confusing the type of lens needed for myopia versus hypermetropia.
  • Incorrectly calculating the focal length or power of the corrective lens.
  • Not clearly defining the 'near point' and 'far point' for a normal eye.

Revision tips

  • Clearly define 'accommodation' and relate it to the ciliary muscles and lens shape.
  • Draw diagrams to illustrate myopia and its correction with a concave lens.
  • Memorize the standard near point (25 cm) and far point (infinity) for a normal eye.

Practice MCQs

Q1. What is the ability of the human eye to adjust its focal length to see both near and distant objects clearly called?

Q2. A person cannot see objects beyond 1.2 meters distinctly. This defect is known as:

Q3. What type of lens is used to correct myopia?

Q4. For a normal human eye, what is the far point?

Q5. What is the minimum distance at which a normal human eye can see an object distinctly without strain?

Frequently asked questions

What is the power of accommodation of the eye?

The power of accommodation is the human eye's ability to adjust the focal length of its lens, allowing it to focus on objects at different distances, both near and far, by changing the thickness of the lens via ciliary muscles.

What is myopia and how is it corrected?

Myopia is a vision defect where a person cannot see distant objects clearly. It occurs when the image is formed in front of the retina. It is corrected using a concave lens, which diverges the light rays before they enter the eye, ensuring the image is focused on the retina.

What are the near point and far point of a normal human eye?

The near point is the minimum distance at which an object can be seen distinctly without strain, which is 25 cm for a normal eye. The far point is the maximum distance at which an object can be seen clearly, which is infinity for a normal eye.

Why does a student sitting in the last row have difficulty reading the blackboard?

This difficulty indicates the student is likely suffering from myopia, a condition where distant objects appear blurred because the eye cannot focus light from them correctly onto the retina.

What is the function of the ciliary muscles in the eye?

Ciliary muscles control the shape of the eye lens. When viewing distant objects, they relax, making the lens thinner. When viewing near objects, they contract, making the lens thicker, thus adjusting the focal length.

Important links

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