Got to know a lot of facts about human eyes, and I am really thankful to BYJU’S for this. Having different refractive indexes is what bends the rays to form an image. 4. The large numbers of light sensitive cells contained in the retina of the eye are of two types: rod shaped cells which respond to brightness or intensity of light and cone shaped cells, which respond to colour of light. Here, the pupil of an eye provides a variable aperture, whose size is controlled by iris. 9. 34. It consists of a convex lens made up of living tissues. He tried to split the spectrum of white light more by using another similar prism, but he could not get any more colours. Correction: Since a convex lens has the ability to converge incoming rays, it can be used to correct this defect of vision, as you already have seen in the animation. (ii) elongation of eyeball. person’s far point Focal length, f =? 3. Correction: Since a concave lens has an ability to diverge incoming rays, it is used to correct this defect of vision. So no vision is possible at that point and is known as a blind spot. It is formed due to the dispersion of sunlight by the tiny water droplet, present in the atmosphere. In this case, Thanks,This app is very good, you have helped me and my friends a lot, I have answered the question easily, that too without any mistake. Object distance, u = -25 cm, normal near point By donating our eyes after we die, one pair of our eyes can give vision to two corneal blind people. To correct Presbyopia, an old person has to use spectacles with a convex lens of suitable focal length, or power as explained already. 11.2 Defects of Vision And Their Correction. the vision of the eye decreases, leading sometimes to total loss of vision. Besides, these sense organs are pretty much similar to cameras, and they help us see objects when light coming from outside enters into them. Tyndall Effect: When a beam of light strikes, the minute particle of earth’s atmosphere, suspended particles of dust and molecule of air the path of beam become visible. Different colours move with same speed in air/vacuum. At ‘A’ – Refraction and dispersion take place. The distance between far point and near point of the eye is called range of vision of the eye. 20. Hence, at noon, the sun appear white as only little of the blue and violet colours are scattered. (i) excessive curvature of the cornea. The maximum focal length (due to excessive curvature of the cornea) of the lens is insufficient to produce a clearly formed image on the retina. The violet light bends the least while the red bends most. Astigmatism can be corrected with lenses having different curvatures in two mutually perpendicular directions i.e., cylindrical lens. This defect is known as Colour Blindness. CBSE Class 10 Science Notes Chapter 11 Human Eye and Colourful World. The temperature and density of different layer of atmosphere keeps varying. Myopia is due to 2. Class 10 Physics Chapters CHAPTER 10: Light-Reflection and Refraction. Covers the outer surface (visible part) of the eye. Why the danger signal or sign is made of red colour? Due to decrease in power (or increase in focal length) of eye lens. 7. Colour blindness is a genetic disorder which occurs by inheritance. 32. The light rays finally are received and focused on the retina. This defect is due to the following reasons : 12. In case of a concave lens, the image is formed in front of the lens i.e., on the same side of the its power of accommodation at old age. Ciliary muscles: These are the muscles which are attached to eye lens and can modify the shape of eye lens which leads to the variation in focal lengths. Dispersion of light is the phenomenon of splitting of white light into its constituent seven colours on passing through a glass prism. Defects of Vision and their Correction Hence, different colours emerge from the prism along different directions. Human eye is nearly spherical in shape of diameter about 2.5 cm. It consists of the following parts: At the junction of the optic nerve and retina, there are no sensory nerve cells. The Lens formula, \(\frac { 1 }{ v } -\frac { 1 }{ u } =\frac { 1 }{ f }\) can be used to calculate the focal length and hence, the power of the myopia correcting lens. Planets are closer to earth and are seen as extended source of light i.e. Rainbow: It is the spectrum of sunlight in nature. As a result, different colours undergo different deviations on passing through the prism. Due to the dispersion of light and internal reflection, different colours reach the observer’s eye. 29. He concluded that Sun is made up of seven visible colour VIBGYOR. For a normal human eye, this distance is around 25 cm. CBSE 10 Science Human Eye and Colourful World. Image distance, v = defective near point Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea. A rainbow is always formed in a direction opposite to that of Sun. This problem is called a cataract. 6. It allowed all the colours of spectrum to pass through second prism. Reason. It contains rods and cones. Accommodation: The ability of the eye to focus both near and distant objects, by adjusting its focal length, is called the accommodation of the eye or the ability of the ciliary muscles to change the focal length of the eye lens is called accommodation. Aqueous humour: It is fluid which fills the space between cornea and eye lens. Captures the light rays focussed by the lens and sends impulses to the brain via the optic nerve. At ‘C’ – Refraction and dispersion take place. Power of the correcting convex lens: The sequence of colours remembers as VIBGYOR. the collection of large number of point sized sources of light. It is like a camera which has a lens and screen system. Chapter wise Physics Quiz for class 8. 21. The human eye has the following parts : 5. Apparent flattering of the Sun’s disc at sunset and sunrise is due to atmospheric refraction. Twinkling of Star: It is also due to atmospheric refraction. Distant star act as point source of light. The retina contains photoreceptor cells called rods and cones and these basically detect the intensity and the frequency of the light. So basically, light rays that are deflected from or by distant objects land on the retina after they pass through various mediums like the cornea, crystalline lens, aqueous humor, the lens, and vitreous humor. Myopia (short sightedness — the image of distant objects is focussed before the retina) is corrected by using a concave lens of suitable power.