The Human Eye And The Colourful World PDF

The Human Eye And The Colourful World Overview The human eye is a sensitive sense organ that helps us see the world and its colors. It works like a camera, forming an image on the retina, a light-sensitive screen. Key Parts: ○ Cornea: Transparent bulge allowing light e...

The Human Eye And The Colourful World Overview The human eye is a sensitive sense organ that helps us see the world and its colors. It works like a camera, forming an image on the retina, a light-sensitive screen. Key Parts: ○ Cornea: Transparent bulge allowing light entry; most refraction happens here. ○ Iris: Dark muscular diaphragm controlling pupil size. ○ Pupil: Regulates light entering the eye. ○ Retina: Delicate membrane with light-sensitive cells generating electrical signals sent to the brain via the optic nerve. ○ Crystalline Lens: Adjusts focal length for focusing objects. Power of Accommodation The eye lens adjusts its focal length to focus on objects at varying distances, controlled by ciliary muscles. ○ Distant Objects: Ciliary muscles relax → lens becomes thinner → focal length increases. ○ Nearby Objects: Ciliary muscles contract → lens becomes thicker → focal length decreases. Least Distance of Distinct Vision (Near Point): ○ Minimum distance to see clearly without strain = 25 cm (for normal eyes). Far Point: ○ Farthest distance for clear vision = infinity (for normal eyes). Cataract Occurs when the lens becomes milky and cloudy with age, causing partial or complete vision loss. Vision can be restored via cataract surgery. Notes on Defects of Vision and Their Correction 1. Refractive Defects of Vision Three common defects: 1. Myopia (Near-sightedness) ○ Symptoms: Can see nearby objects clearly; distant objects appear blurry. ○ Causes: Excessive curvature of the eye lens. Elongation of the eyeball. ○ Effect: Far point is closer than infinity; image forms in front of the retina. ○ Correction: Use of concave lenses to bring the image back to the retina. 2. Hypermetropia (Far-sightedness) ○ Symptoms: Can see distant objects clearly; nearby objects appear blurry. ○ Causes: Focal length of the lens is too long. Eyeball is too small. ○ Effect: Near point is farther than normal (beyond 25 cm); image forms behind the retina. ○ Correction: Use of convex lenses to focus light on the retina.  3. Presbyopia ○ Symptoms: Difficulty in seeing nearby objects due to aging. ○ Causes: Weakening of ciliary muscles. Loss of flexibility in the eye lens. ○ Correction: Use of bi-focal lenses: Upper part (concave lens) for distant vision. Lower part (convex lens) for near vision. 2. Correction Options Eye-glasses with spherical lenses (concave/convex). Contact lenses. Surgical interventions (e.g., LASIK). 3. Key Definitions Power of Accommodation: Ability of the eye to adjust its focal length for clear vision at various distances.  Near Point: Closest distance for clear vision (25 cm for a normal eye). Far Point: Farthest distance for clear vision (infinity for a normal eye). 4. Eye Donation Eyes can be donated after death to restore vision for those with corneal blindness. Eye donors can be of any age or gender, even those with glasses, cataract, or certain medical conditions. Remove eyes within 4-6 hours after death. Process: 10-15 minutes, no disfigurement. Eligible: Any age, spectacles, cataract, diabetes, etc. Ineligible: AIDS, Hepatitis, rabies, etc. Impact: One pair restores vision for 4 people. Eye banks handle collection, evaluation, and research. Refraction and Dispersion of Light 10.3 Refraction of Light Through a Prism A triangular prism has two triangular bases and three inclined rectangular surfaces. Angle of the prism: The angle between two lateral faces. Refraction in a prism: ○ Light bends towards the normal when entering glass (denser medium). ○ Light bends away from the normal when exiting into air (rarer medium). Angle of Deviation (∠D): The angle between the incident ray and the emergent ray. 10.4 Dispersion of White Light by a Prism Dispersion: Splitting of white light into its component colors. Spectrum: Band of colors (VIBGYOR – Violet, Indigo, Blue, Green, Yellow, Orange, Red). ○ Red: Bends the least. ○ Violet: Bends the most.  Newton’s Experiment: ○ Used two prisms to prove that sunlight is made of seven colors. ○ White light re-emerges when spectrum passes through an inverted prism. Rainbow Formation: ○ Caused by: Dispersion of sunlight by tiny water droplets. ○ Process: 1. Refraction and dispersion at droplet's surface. 2. Internal reflection. 3. Refraction upon exiting. ○ Seen: In a direction opposite to the Sun, e.g., after rain or near waterfalls. —------------------------------------------------------------------------- Atmospheric Refraction and Scattering of Light 10.5 Atmospheric Refraction  Definition: Refraction of light by the Earth's atmosphere due to varying refractive indices of air layers. Twinkling of Stars: ○ Caused by atmospheric refraction of starlight. ○ Starlight bends towards the normal, making stars appear slightly higher than their actual position. ○ Stars twinkle because their light fluctuates due to atmospheric instability. Planets Do Not Twinkle: ○ Planets are closer and appear as extended sources; light from multiple points averages out, nullifying twinkling. Advance Sunrise and Delayed Sunset: ○ Sun appears 2 minutes earlier (sunrise) and sets 2 minutes later (sunset) due to atmospheric refraction. ○ Apparent flattening of the Sun’s disc during sunrise and sunset is due to the same phenomenon. 10.6 Scattering of Light Tyndall Effect: ○ Scattering of light by colloidal particles makes the path of light visible. ○ Observed in smoke-filled rooms or sunlight passing through dense forest canopies. ○ Larger particles scatter longer wavelengths; finer particles scatter shorter wavelengths (e.g., blue). Why is the Sky Blue? ○ Fine particles in the atmosphere scatter shorter wavelengths (blue) more than longer wavelengths (red). ○ Without the atmosphere, the sky would appear dark (e.g., at high altitudes). Red Colour for Danger Signals: ○ Red light scatters the least and is visible over longer distances, even in fog or smoke _________________________________________________________________________. Short Notes: The Eye and Vision Defects Accommodation of the Eye: ○ Ability of the eye to focus on near and distant objects by adjusting its focal length. Near Point of the Eye: ○ Closest distance for clear vision without strain. ○ For a young adult: 25 cm.  Common Vision Defects: ○ Myopia (Short-Sightedness): Distant objects' images focus before the retina. Corrected with a concave lens. ○ Hypermetropia (Far-Sightedness): Nearby objects' images focus beyond the retina. Corrected with a convex lens. ○ Presbyopia: Loss of accommodation with age; requires bifocal lenses. Dispersion: ○ Splitting of white light into its component colors. Scattering of Light: ○ Responsible for the blue color of the sky.