Bright Tutorials Bright Tutorials
CBSE Class 10 Science Question 2 of 12

The Human Eye and the Colourful World — Question 5

Back to all questions
5
Question

Question 5

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

Power is reciprocal of focal length.

(i) Focal length of the lens required for correcting distant vision = −15.5-\dfrac{1}{5.5} = -0.181 m = -18.1 cm

(ii) Focal length of the lens required for correcting near vision = 11.5\dfrac{1}{1.5} = 0.667m = 66.7cm

Web Content: The Human Eye and the Colourful World | Bright Tutorials
BRIGHT TUTORIALS
Bright Tutorials Logo
BRIGHT TUTORIALS
CBSE Class X | Academic Year 2026-2027
9403781999
Excellence in Education
Science | Chapter 10: The Human Eye and the Colourful WorldWeb Content

Chapter 10: The Human Eye and the Colourful World — Quick Revision Guide

Introduction

The human eye is a natural optical instrument. This chapter explains how the eye works, defects of vision and their correction, and beautiful phenomena like dispersion, atmospheric refraction, and scattering of light.

Key Points at a Glance

  1. Eye: cornea (refraction) → iris/pupil (light control) → lens (fine focus) → retina (image) → optic nerve → brain
  2. Accommodation: eye lens changes focal length using ciliary muscles; near point = 25 cm, far point = ∞
  3. Myopia: can't see far; image before retina; corrected by concave lens
  4. Hypermetropia: can't see near; image behind retina; corrected by convex lens
  5. Presbyopia: age-related; corrected by bifocal lens; Cataract: opaque lens; corrected by surgery
  6. Dispersion: white light splits into VIBGYOR through prism; violet deviates most, red least
  7. Atmospheric refraction: twinkling of stars, advanced sunrise/delayed sunset (~2 min each)
  8. Scattering: intensity ∝ 1/λ4; blue sky (short λ scattered more); red sunrise/sunset (blue scattered away); white clouds (all λ scattered equally by large droplets)
  9. Tyndall effect: scattering by colloidal particles; visible beam in dusty room, fog

Real-World Connections

Eye donations restore sight; LASIK surgery reshapes cornea; blue colour of sky and red sunsets explained by scattering; danger signals are red because red light travels farthest.

Quick Self-Test (5 Questions)

  1. What is the most important concept you learned from this chapter?
  2. Can you write three key equations/formulae from this chapter from memory?
  3. Draw a labelled diagram relevant to this chapter without looking at your notes.
  4. Explain one real-world application of a concept from this chapter.
  5. What is one common mistake students make in this chapter, and how can you avoid it?

Further Study

  • NCERT Textbook Chapter 10
  • NCERT Exemplar Problems
  • Bright Tutorials Detailed Notes: ch10-human-eye.html
  • Bright Tutorials Practice Questions: ch10-human-eye.html
  • Previous Year CBSE Board Papers

Bright Tutorials | Hariom Nagar, Nashik Road | 9403781999 | brighttutorials.in