Human Eye and Colorful World PDF

## ALAKH sir ke FARREY ### HUMAN EYE AND COLOURFUL WORLD **(1) Eyeball:** Approximately spherical, Diameter 2-3cm **(2) Cornea:** - Thin transparent - bulging membrane - Most of the refraction happens - Protects from dust, germs **(3) Iris:** - Controls the size of pupil. - Regulates and control...

## ALAKH sir ke FARREY ### HUMAN EYE AND COLOURFUL WORLD **(1) Eyeball:** Approximately spherical, Diameter 2-3cm **(2) Cornea:** - Thin transparent - bulging membrane - Most of the refraction happens - Protects from dust, germs **(3) Iris:** - Controls the size of pupil. - Regulates and controls the amount of light entering the eye. **(4) Pupil:** **(5) Crystalline lens:** - Convex lens - Flexible focal length. - Forms Real and Inverted image **(6) Ciliary Muscles:** - Adjust the focal length of eye lens. **(7) Retina:** - Real Inverted Image is formed on Retina. - Has lots of light sensitive cells. - Rods- vision in low light (light Intensity) - Cones - vision in high light + colour vision - Cells get activated when light falls on them and generates electrical signal. **(8) Optical nerve:** - Sends electrical signal to the brai- **(9) Aqueous Humour** - Water like fluid. - It is present between lens and Cornea. - Nutrition. **(10) Vitreous Humour** - Gel like substance. - Present between lens and Retina. - Support and strength helps the eye to keep its shape. ### Power of Accomodation The ability of eye lens to adjust/change its focal length. **NEAR POINT:** The minimum distance from eye at which an object can be seen clearly and distinctly. It is also called Least Distance of Distinct vision. For normal vision (young adults)-25cm **FAR POINT:** The farthest (sabse door) point upto which the eye can see objects clearly. For normal eyes infinity. **(a) Converging Lens:** - f +ve - p +ve **(b) Concave Lens:** - f -ve - p -ve **(c) Convex lens:** - p + ### DEFECTS in HUMAN EYE And ### Corrections **(1) Myopia** **(Near Sightedness)** - Can see nearby objects clearly. - Cannot see distant objects distinctly (clearly) - Far point is less than infinity. - Image of distant object is formed in front (before) of Retina. **Reasons:** - Excessive curvature of eye lens. - Lens thick Focal length decreases - Elongation of eye ball. **Correction - CONCAVE Lens** - Trick: MyoNi makes Elon Thick, went CAVE ↓ Myopla Near Sightedness of eyeball **(2) Hypermetropia** **(far-sightedness)** - Can see distant (far) objects clearly. - Cannot see nearby objects distinctly(clearly) - Near point is more than 25cm. - Image of nearby object is formed at a point behind retina. **Reason:** - Focal length of eye lens is too long (lens cannot get thick enough) - Eyeball has become too small. **Correction - CONVEX Lens** - Trick: Fast Metro makes eye small, Face Large like Wax ↓ Far Sightedness ↓ Eyeboll Smoll Shrink ↓ Focal Length Large Thin **(3) Presbyopia** - With ageing people find it difficult to see nearby objects distinctly (clearly). Generally they also have trouble to - Reason: - Weakening of ciliary muscle. - Less Flexibility of eye lens. - Lens becomes opaque. - Sometimes at old ages Crystalline lens becomes milky and cloudy - Partial or complete loss of vision **Correction: CATARACT SURGERY** - Solution: - Bifocal Lenses ### REFRACTION OF LIGHT & ### DEVIATION THROUGH A PRISM **Monochromatic light:** - <i → incidence - <r → Refraction - <e → emergence - <D → Deviation - Angle of prism - A **A prism bends a ray of light towards its Base.** **We know that white light is made up of seven colours.** **Angle of Deviation (<D)** - <D is different for different colours of light, some colours bend more than other - Red Bends LEAST - Violet Bends MORE ### Refraction of whitelight (sunlight) through a PRISM. **Dispersion:** - The splitting of white light It into its component colours (7 colors) **Spectrum:** - The band of color components of light (obtained on screen) **NEWTON'S PRISM EXPERIMENT (CINVERTED PRISMS)** - White Light (Sunlight) consists of 7 colours ### RAINBOW FORMATION - Dispersion + Refraction + Reflection ### ADVANCE SUNRISE AND DELAY SUNSET - Sun is visible 2 mins Before actual sunrise - Sun is visible for 2 extra mins after actual Sunset ### Twinkling of stars - The physical conditions like temperature, pressure of earth 's atmosphere keeps on varying. - Due to this density of layers also keep changing. - Stars are very far so they behave like point source of light. - The path of ray of light coming from star keeps changing and Amount of starlight entering eyes flickers ### Why Planets Do not twinkle - Planets are near to Earth as compared to stars. - Planets behave as extended source of light. - Extended source can be imagined as Collection of millions of point source of light. - Now, the total variations in the amount of light entering our eye from all the individual point-sized sources Averages out to zero and intensity of light entering eye remains almost same. ### Blue colour of sky - The molecules of air and other pine partides in the atmosphere have size smaller than the wavelength of Visible light. - Scattering is more for light of shorter wavelength Hence Blue colour scatters more strongly than Red colour - Thus, scatters more strongly than Red colour. - Thus, scattered blue light enters our eyes and sky appears blue. ### Reddening of the Sun at Sunrise & Sunset - If the earth had no atmosphere there would not have been any scattering Then the sky would have locked dark. - Astronauts- Dark - The sky appears dark to passengers Flying at very high altitudes. Explain: At high altitudes due to the absence of atmosphere, scattering of light do not take place and hence sky appears dark to passengers Flying at high altitudes. - Danger signal lights are red in colour. Explain: Red light is least scattered by fog or smoke. Therefore, it can be seen in the same colour at a distance. ### TYNDALL EFFECT - The phenomenon of scattering of light by the colloidal particles. - A colloid is a heterogenous mixture. - The size of particles of a colloid is too small to be individually seen with naked eyes - Example: Milk, smoke, Dust in air. - The path of a beam of light passing through a true solution is not Visible. But in colloidal passing through a true solutions colloidal solutions, colloids are big enough to scatter a beam of light passing through it and make its path visible. - The colour of the scattered light depends on the size of the scattering particles. - Very small particles scatter mainly blue light (smallest wave length) - Very large particles scatter all colour of Flight equally ### ATMOSPHERIC REFRACTION - Density of air decreases with height above earth's surface. - Rarer to denser layers of air - Beam of sunlight enters a smoke filled room through a small hole. Sunlight passes through a canopy of a dense forest. Tiny water droplets in the mist scatter light. ### CURRENT YEAR QUESTIONS **(Question-1)** **(a)** Draw schematic diagram of Human Eye and write the function of each part of the human eye. **(b)** A person suffering from both myopia and hypermetropia defects. wh sufferings from both - When does it happen? - Name the type of lens often required by the person sufferings from this defects. - Draw ray diagrams to illustrate correct images, formation in the human eye for the above vision defects (CBSE 2015,2016,2018,2019,2020 **(Question-2)** **(a)** Question: study the diagram given below and answer the question that follows. - Name the defect of vision deficted in this diagram stating the part of the eye responsible for this conditions. - List two causes of this defect. - Name the type of lens and used to correct this defect and explain with diagram. **(b)** A person need a lens of power +3D for correcting his near vision and -3D required to correct these defects. for correcting his distant vision calculate the focal length of the lenses (CBSE 2020,2023, 2024) **(Question-3)** Akshay sitting in the last row in his class, could not see clearly the words written on the blackboard when the teacher noticed it, he announced if any Students: sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher advice Akshay's parents to get his eyesight checked. In the context of the above event, answer the following questions. **(a)** Which defect of visions is Akshay sufferings from? Explain with Diagram. **(b)** Which type of lens is used to correct this defects? Draw a diagram. (CBSE 2015, 2018,2024,2024) **(Question-4)** **(a)** What is dispersion of white light? state its cause. **(b)** Draw gray diagram to show the dispersion of white light by a glass prism. **(c)** White light is dispersed into seven visible coloured components by a glass prism. Name the colour that bends. - The most - The least (CBSE 2012,2017,2023,2024) **(Question-5)** What is rainbow? Draw a labelled diagram to show the formation of grainbow. **(a)** Name the phenomenon of light responsible for the Tyandall effect why is the this effect shown by colloidal particles? **(b)** Mention instances where the Tyndall effect can be observed. **(c)** List the factors on which the scattering of light depends. **(d)** Explain why the apparent position of a object fluctuates or waves when seen through hot air. (CBSE 2012,2015,2019,2020,2024) **(Question-6)** Differentiate between a glass slab and a glass prism . What happens when a narrow beam of **(a)** monochromatic light and **(b)** White light passes through (a) glass slab (b) glass prism ? **(iii)** How can the coloured components of white light be recombined after a prism has separated them? Draw a labelled Diagram to justify your answer ? (CBQ) (CBSE 2023,2020,2024) **(Question-7)** Give reasons for the following. **(a)** Red colour is used for danger signals and installed at airports and the top of tall buildings. **(b)** The sky appears dark to passengers flying at very high altitudes or in space. **(c)** The path of a beam of light passing through a colloidal solution is visible. **(d)** The time difference between actual sunset and apparent sunset is about 2 minutes. (CBSE 2023,2020) **(Question-8)** **(a)** What is atmospheric refraction? Briefly explain why does the apparent position of a star appear different from its true position? **(b)** Explain why the planets do not twinkle but the stars twinkle. (CBSE 2016,2019)