Human Eye and Colorful World Class 10 Notes PDF

CLASS 10 NOTES SCIENCE Human eye and the colourful world PRASHANT KIRAD  PRASHANT KIRAD The Human Eye The human eye is a complex and highly specialized sensory organ responsible...

CLASS 10 NOTES SCIENCE Human eye and the colourful world PRASHANT KIRAD  PRASHANT KIRAD The Human Eye The human eye is a complex and highly specialized sensory organ responsible for the sense of vision. It is one of the primary components of the visual system in humans and plays a crucial role in perceiving the world around us. D Different parts of the human eye : RA KI Part Function/Definition T AN The transparent, dome-shaped surface that covers the front of the Cornea eye and helps to focus incoming light. H AS The colored part of the eye that controls the size of the pupil, Iris regulating the amount of light entering. PR The opening in the center of the iris that allows light to pass Pupil through. A transparent structure behind the pupil that focuses light onto Lens the retina by changing shape. The inner layer at the back of the eye containing light-sensitive Retina cells (rods and cones); converts light into electrical signals. Aqueous and Clear fluids filling the front and back chambers of the eye, Vitreous Humors providing nourishment and maintaining the eye's shape. The nerve that carries visual information from the retina to the Optic Nerve brain for processing.  PRASHANT KIRAD Flow mantra Power of accommodation : D The power of accommodation is the eye's ability to adjust and “Defects Of Vision RA focus on objects at different distances by changing the shape dhyaan mei rakhna of the lens, allowing us to see clearly at various ranges. diagram ke saath” KI Defects of vision and their connections : - Prashant Bhaiya Defects of vision, also known as refractive errors, occur when the eye is unable to T focus light correctly on the retina, leading to blurred or impaired vision. The most AN common types of vision defects are: 1. Myopia (Nearsightedness): Myopia, or H nearsightedness, is a vision condition where AS distant objects appear blurry due to the eye's inability to focus properly on them. PR Causes of myopia: The eyeball is too long, or the cornea is too curved, causing light rays to focus in front of the retina instead of directly on it. Correction: Myopia is usually corrected with concave (diverging) lenses, which spread out the light rays before they enter the eye, allowing them to focus on the retina. 2. Hypermetropia (Farsightedness): It is also known as farsightedness, is a vision condition where distant objects are clearer than close-up objects due to the eye's inability to focus on nearby objects properly. Causes of Hypermetropia: The eyeball is too short, or the cornea is not curved enough, causing light rays to focus behind the retina.  PRASHANT KIRAD Correction: Hypermetropia is corrected with convex (converging) lenses, which bend the light rays inward before they enter the eye, allowing them to focus on the retina. 3. Presbyopia: Presbyopia is an age-related vision condition where it becomes difficult to focus on close-up objects, usually requiring reading glasses for correction. Causes of Presbyopia: The lens of the eye loses its flexibility with age, making it harder to change its shape for focusing on near objects (loss of power of accomodation). Correction: Presbyopia is often corrected with reading glasses, bifocal lenses, or progressive lenses. D RA KI Prism JOSH METER? T AN A transparent refracting medium bounded by at least two lateral surfaces inclined to each other at a certain angle. H AS Dispersion of white light by a glass prism PR A glass prism disperses white light, splitting it into its constituent colors, and creating a rainbow-like spectrum due to the varying refraction of different wavelengths of light.  PRASHANT KIRAD Why dispersion occur? Dispersion of light occurs when white light passes through a prism because different colors (wavelengths) of light are refracted, or bent, by different amounts. Recombination of the spectrum of white light: Recombination of white light involves merging the separated colors (spectrum) created by a prism or similar device, resulting in the restoration of white light. BGYO Rainbow VI R D A rainbow is a natural optical phenomenon that occurs when sunlight is dispersed, RA refracted, and reflected by water droplets in the atmosphere, creating a spectrum of light in the form of a circular arc. KI Rainbow formation: After rain, there are many tiny droplets of water T still in the air AN When sunlight falls on these droplets These droplets act as tiny prisms H When sunrays fall on these droplets, the rays get first refracted, then internally reflected and AS then refracted again Due to this different colors of sunlight are bent PR at different angles and we are able to see a spectrum in the form of a rainbow EMA Atmospheric refraction: When refraction occurs between two mediums, and one of these mediums is Earth's atmosphere, this phenomenon is referred to as atmospheric refraction. Consequences of Atmospheric Refraction: Atmospheric refraction Twinkling of stars Planet do not Twinkle Stars seem higher than they actually appear Advance sunrise and Delayed sunset  PRASHANT KIRAD Concept Explanation Twinkling is caused by the bending of starlight as it passes through Earth's Twinkling of atmosphere, due to variations in the atmosphere's refractive index. This leads Stars to rapid fluctuations in a star's apparent position and brightness. Light from stars undergoes refraction as it enters Earth's atmosphere, Stars Seem bending towards the normal with each layer. This atmospheric refraction Higher than causes the apparent position of a star to be slightly higher than its actual They Appear position, especially when viewed near the horizon. Planets appear as small disks and reflect the Sun's light, providing a more Planets Do stable and constant source of illumination. This prevents the twinkling effect, Not Twinkle unlike distant stars, which are point sources of light. D Advance The Sun can be seen approximately two minutes before it officially rises and RA Sunrise and about two minutes after it technically sets. This is due to atmospheric Delayed refraction, which bends the Sun's light, allowing it to be visible even when it is KI Sunset below the horizon. “Bahut Jaroori Table” T - Prashant Bhaiya Scattering of light: AN Scattering of light is the process by which light rays are redirected in different directions as they pass through particles in the atmosphere or H another medium. This phenomenon occurs because light interacts with small AS particles or molecules, causing the light to spread out in various directions. Scattering of light depends on the type of particles: PR Very fine particles scatter mainly in blue colour. Large sized particle scatter light of longer wavelength Shorter wavelength greater will be the scattering Consequences of scattering of light: VIP (very important portio n) Scattering of light Tyndall Effect Blue Sky Colour of sun During sunrise The scattering of light by and sunset Air molecules and tiny tiny particles in Earth's Light travels a longer path particles in the atmosphere atmosphere, such as smoke, through the atmosphere, scatter shorter-wavelength water droplets, and dust, scattering shorter blue light more effectively making these particles wavelengths like blue, and than longer-wavelength red visible. allowing the red and orange light, making the scattered colors to dominate.. blue light reach our eyes.  PRASHANT KIRAD #TOP 7 IMPORTANT QUESTIONS 1) "A person cannot read a book at distances less than 50 cm. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams to show the image formation: a. by defective eye b. after using a corrective lens Solution: a. Either the hypermetropic eyeball is too short or corea is too curved. b. The ciliary muscle is unable to change the shape of the lens enough to properly focus the image i.e., the focal length of the eye lens is too long. This defect is called hypermetropia. D 2) (a) If a person wears a lens of power - 6D for distant vision and for correcting his near vision he needs a lens of +2D. Determine the focal length of the lenses in both cases. [CBSE 2016] RA (b) Give a reason for the following natural phenomenon: KI (i) Stars twinkle (ii) Planets do not twinkle T (iii) Stars appear raised in the sky. AN Solution: H AS PR (b) (i) Due to continuous changes in the densities of the atmospheric layers the apparent position of the star also changes; which makes the light coming from the distant point-sized star brighter and dimmer. The light coming from the stars therefore gives a shaking appearance, which gives the impression of the twinkling of a star. (ii) Since the planets are closer to us. Due to this they appear a combination of large point-size source of light, and change in the path of light coming from the planets is not significant. So planets do not appear twinkling. (iii) Due to atmospheric refraction, a star appears to be slightly higher than its actual position in the sky. 3) a) Explain why colour of the sky appears blue during the day with the help of a diagram. (b) Explain why the Sun looks reddish at the time of sunrise and sunset.  PRASHANT KIRAD Solution: (a) Due to the scattering of blue colours by the dust particles present in the atmosphere. (b) During the Sunrise or Sunset, Sun is at the horizon, and sunlight travels a longer distance in the atmosphere. Due to this, all colours get scattered except red which reaches the eye of the observer to whom sun appears reddish in the morning or evening. 4) Why do stars twinkle? Explain. Light coming from stars when enters the Earth's atmosphere suffers Solution: D refraction from the atmospheric layers. Since the densities of atmospheric gases change frequently. Since the stars are point-sized and at a far RA distance sometimes stars appear brighter and sometimes dimmer which gives the impression as the stars twinkling. KI 5) (a) What is the least distance of distinct vision for the normal eye? T (b) Does the above distance increase or decrease for long sighted eye? Give a reason AN for your answer with a diagram. Solution: H (a) For a normal human eye, the least distance of distinct vision AS is 25 cm. (b) Least distance of distinct vision increases for long-sighted PR eyes. A hypermetropic eye can see up to an infinite distance, which is more than 25 cm. 6) With the help of a diagram, Explain the formation of a rainbow in the sky. Solution: The water droplets in the atmosphere act like small prisms. These droplets refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop. Due to the distortion of sunlight and internal reflection, different colours reach the observer.  PRASHANT KIRAD 7. A person with a defective eye-vision is unable to see objects nearer than 1.5 m. He wants to read books at a distance of 30 cm. Find the nature, focal length, and power of the lens he needs in his spectacles. (CBSE 2016) Solution: D RA KI T AN “Class 10th Phodenge” - Prashant Bhaiya H AS PR