The Human Eye and the Colourful World

Class 10 Science • Chapter 11

Chapter Overview

This chapter explains the human eye and how it enables us to see objects. It covers the structure and functions of the eye, power of accommodation, near point and far point, defects of vision and their correction.

The chapter also explains refraction through a prism, dispersion of white light, atmospheric refraction, twinkling of stars, advanced sunrise, delayed sunset, scattering of light and related natural phenomena.

📘 Complete Notes

Detailed notes on the human eye, accommodation, defects of vision, prism, dispersion, atmospheric refraction and scattering of light.

❓ Important Questions

Conceptual, reasoning, diagram-based and competency-focused questions for examination preparation.

📝 Previous Year Questions

Chapter-focused previous year questions and exam-oriented practice resources.

🔢 Numericals

Lens power, focal length and vision-correction based numerical questions with step-by-step solutions.

Topics Covered

The Human Eye

Structure of Human Eye

Functions of Different Parts of Eye

Cornea

Iris and Pupil

Eye Lens

Retina

Optic Nerve

Power of Accommodation

Near Point

Least Distance of Distinct Vision

Far Point

Myopia

Causes of Myopia

Correction of Myopia

Hypermetropia

Causes of Hypermetropia

Correction of Hypermetropia

Presbyopia

Correction of Presbyopia

Refraction Through a Prism

Angle of Deviation

Dispersion of White Light

Spectrum

VIBGYOR

Formation of Rainbow

Atmospheric Refraction

Twinkling of Stars

Advanced Sunrise

Delayed Sunset

Scattering of Light

Blue Colour of the Sky

Reddish Sun at Sunrise and Sunset

Tyndall Effect

Applications of Atmospheric Refraction

Quick Revision

The human eye forms an image on the retina.
Accommodation is the ability of the eye lens to adjust its focal length for clear vision.
The near point of a normal young adult eye is approximately 25 cm.
The far point of a normal eye is approximately infinity.
Myopia is corrected using a suitable concave lens.
Hypermetropia is corrected using a suitable convex lens.
Presbyopia is associated with reduced accommodation with advancing age.
A prism can produce dispersion of white light into its constituent colours.
Atmospheric refraction is responsible for phenomena such as twinkling of stars and advanced sunrise.
Scattering of light explains phenomena such as the blue colour of the sky.

Important Formulae

P = 1/f

Power of a lens when focal length f is in metres.

f = 1/P

Focal length from power of a lens.

1/f = 1/v - 1/u

Lens formula used in vision-correction numericals.

m = hᵢ/hₒ = v/u

Magnification of a lens.

n = c/v

Refractive index of a medium relative to vacuum.

Defects of Vision

Defect	Main Problem	Common Cause	Correction
Myopia	Distant objects are not clearly visible.	Excessive convergence or elongated eyeball.	Concave lens.
Hypermetropia	Nearby objects are not clearly visible.	Insufficient convergence or shorter eyeball.	Convex lens.
Presbyopia	Difficulty in accommodation with age.	Reduced flexibility of lens and related changes.	Suitable corrective lenses.

Atmospheric Refraction & Scattering

Phenomenon	Main Cause	Explanation
Twinkling of Stars	Atmospheric Refraction	Changing atmospheric conditions produce changing apparent position and brightness.
Advanced Sunrise	Atmospheric Refraction	The Sun can be seen slightly before its geometrical rise.
Delayed Sunset	Atmospheric Refraction	The Sun may remain apparently visible slightly after its geometrical setting.
Blue Colour of Sky	Scattering of Light	Shorter-wavelength components are scattered more strongly.
Reddish Sun	Scattering of Light	The longer atmospheric path enhances the relative prominence of longer-wavelength light.

Dispersion of White Light

When white light passes through a prism, its constituent colours can separate because different colours undergo different amounts of deviation in the prism. This phenomenon is called dispersion.

Spectrum: The band of colours obtained after dispersion of white light is called the spectrum.

The commonly remembered sequence of visible colours is: VIBGYOR — Violet, Indigo, Blue, Green, Yellow, Orange and Red.

Formation of Rainbow

A rainbow is a natural optical phenomenon produced when sunlight interacts with water droplets in the atmosphere. Refraction, dispersion and internal reflection of light within droplets contribute to the observed coloured arc.

Remember: Rainbow formation involves refraction, dispersion and internal reflection.

🎯 Exam Focus:

Human eye का labelled diagram, accommodation, Myopia, Hypermetropia और Presbyopia के correction diagrams, prism and dispersion, rainbow formation, atmospheric refraction, twinkling of stars, advanced sunrise, delayed sunset, scattering और blue sky से जुड़े questions को विशेष रूप से prepare करें।

🔢 Numerical Focus:

Lens power, focal length, lens formula और vision-correction based numericals में units तथा sign convention को carefully apply करें।

Official Study Sources

Use official NCERT and CBSE Academic resources for curriculum-aligned study and textbook reference.

NCERT Official Website → CBSE Academic Website → CBSE Academic Curriculum 2026-27 →