Ch 11 covers the human eye, defects of vision and their correction, and optical phenomena — dispersion through a prism, rainbow formation, atmospheric refraction, and Tyndall scattering.
Light enters through cornea → passes through pupil (iris controls size) → lens focuses on retina → rods/cones detect light → optic nerve sends signals to brain. Accommodation: ciliary muscles change lens shape to focus on objects at different distances. Near point: 25 cm. Far point: infinity.
Myopia (near-sightedness): distant objects blurry; image forms before retina. Cause: elongated eyeball or thick lens. Correction: concave lens. Hypermetropia (far-sightedness): near objects blurry; image forms behind retina. Cause: short eyeball or thin lens. Correction: convex lens. Presbyopia: loss of accommodation in old age; corrected by bifocal lens.
Dispersion: splitting of white light into spectrum (VIBGYOR) by a prism. Each colour has different wavelength (violet shortest, red longest) — different refraction. Rainbow: dispersion + internal reflection in raindrops. Scattering: tiny particles scatter shorter wavelengths more (Rayleigh scattering). Blue sky: air molecules scatter blue light. Red sunset: long path → blue scattered away → red/orange reach eyes.
Download: https://ncert.nic.in/textbook/pdf/jesc111.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jesc1ps.zip
At sunrise/sunset, sunlight travels a longer path through the atmosphere. Most of the blue light is scattered away by air molecules during this long journey. Only red and orange light (longer wavelengths, less scattered) reach our eyes directly, making the Sun appear reddish.
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