Class 10 Science Chapter 10 Human Eye Revision Notes

Class 10 Science Chapter 10 – The Human Eye and the Colourful World: Quick Revision Notes

Power of accommodation: ability of the eye lens to adjust focal length via ciliary muscles
Near point (normal eye) ≈ 25 cm; Far point (normal eye) = infinity
Myopia (near-sightedness): distant objects blurred, far point < infinity → corrected with a concave (diverging) lens
Hypermetropia (far-sightedness): near objects blurred, near point > 25 cm → corrected with a convex (converging) lens
Presbyopia: age-related loss of accommodation → corrected with bifocal lenses
Power of a lens: P = 1/f (f in metres); unit = dioptre (D)
Concave lens → negative power; Convex lens → positive power
Atmospheric refraction: bending of light due to continuously varying density of air
Twinkling of stars: caused by atmospheric refraction of starlight through layers of varying density
Planets do not twinkle: extended sources, twinkling effects of many points average out
Advance sunrise / delayed sunset: each about 2 minutes, due to atmospheric refraction
Tyndall effect: scattering of light by colloidal-sized particles
Blue colour of sky: shorter wavelengths (blue/violet) scattered more by atmospheric molecules
Reddish sun at sunrise/sunset: longer atmospheric path scatters away blue light, red light reaches the eye
Sky appears black to astronauts: no atmosphere at high altitude to scatter sunlight