Chapter 10 — The Human Eye and the Colourful World

Class 10 Science Chapter 10 covers the human eye's structure and defects of vision, dispersion of white light through a prism, atmospheric refraction phenomena like twinkling of stars, and why the sky appears blue due to scattering of light.

Chapter 10 of NCERT Class 10 Science explores the human eye as a camera-like optical instrument, explaining how the crystalline lens and ciliary muscles enable accommodation to focus on near and distant objects. It covers three refractive defects — myopia (corrected by concave lens), hypermetropia (corrected by convex lens), and presbyopia — and their corrections. The chapter also explains dispersion of white light into VIBGYOR through a prism, rainbow formation by water droplets, twinkling of stars due to atmospheric refraction, and the blue colour of the sky caused by scattering of shorter wavelengths of light (Tyndall effect).

1. 01The human eye uses a crystalline lens and ciliary muscles to adjust focal length, enabling accommodation for objects from 25 cm (near point) to infinity (far point).
2. 02Myopia (near-sightedness) is corrected with a concave lens; hypermetropia (far-sightedness) is corrected with a convex lens; presbyopia (age-related) often requires bi-focal lenses.
3. 03A glass prism splits white light into seven colours — Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR) — because different colours bend through different angles.
4. 04A rainbow is formed when water droplets in the atmosphere refract, internally reflect, and disperse sunlight, and is always seen in the direction opposite the Sun.
5. 05Stars twinkle due to continuous atmospheric refraction of starlight, while planets do not twinkle because they appear as extended sources whose variations average out to zero.
6. 06The sky appears blue because fine atmospheric particles scatter shorter wavelengths (blue light) more strongly than longer wavelengths (red light).