12.15 Human eye 10th physics. Accommodation nearsightedness and farsightedness. In urdu hindi, Queries solved in this video atifahmedofficial atifahmadofficial 1. What is eye 2. How image form in eye 3. What is accommodation 4. What is near point 5. What is far point 6. What is accommodation 7. What is lens accommodation Related searches 1. Human eye 2. Human eye in urdu 3. Human eye in hindi 4. Human eye 10th class physics 5. Human eye physics 6. 12.15 human eye 7. Human eye sabaq 8. Human eye khan 9. Human eye ilm 10. Accommodation 11. Accommodation in urdu 12. Lens accommodation 13. What is lens accommodation 14. Near and far point GEOMETRICAL OPTICS Not For Sale – PESRP 59 Fig.12.35: Image formation in human eye Retina Iris Lens Object Cornea Light rays Quick Quiz How the size of the pupil of our eye will change: (a) in dim light? (b) in bright light? Image Distant object Close object Tensed lens Image on retina Image on retina Relaxed lens (a) (b) 12.15 THE HUMAN EYE The image formation in human eye is shown in Fig.12.35. Human eye acts like a camera. In place of the film, the retina records the picture. The eye has a refracting system containing a converging lens. The lens forms an image on the retina which is a light sensitive layer at the back of the eye. In the camera, the distance of lens from film is adjusted for proper focus but in the eye, the lens changes focal length. Light enters the eye through a transparent membrane called the cornea. The iris is the coloured portion of the eye and controls the amount of light reaching the retina. It has an opening at its centre called the pupil. The iris controls the size of the pupil. In bright light, iris contracts the size of the pupil while in dim light pupil is enlarged. The lens of the eye is flexible and accommodates objects over a wide range of distances. Accommodation The camera focuses the image of an object at a given distance from it by moving the lens towards or away from the film. The eye has different adjusting mechanism for focusing the image of an object onto the retina. Its ciliary muscles control the curvature and thus the focal length of the lens, and allow objects at various distances to be seen. Fig.12.36: Human eye accommodation If an object is far away from the eye, the deviation of light through the lens must be less. To do this, the ciliary muscles relax and decrease the curvature of the lens, thereby, increasing the focal length. The rays are thus focused onto the retina producing a an object is close to the eye, the ciliary muscles increase curvature of the lens, thereby, shortening the focal length. The divergent rays from the nearer object are thus bent more so as to come to a focus on the retina (Fig.12.36-b). The variation of focal length of eye lens to form a sharp image on retina is called accommodation. It is large in young people while it goes on decreasing with age. Defects in accommodation may be corrected by using different type of lenses in eyeglasses. In the following sections, we will describe defect of vision and their remedies. Near Point and Far Point When we hold a book too close, the print is blurred because the lens cannot adjust enough to bring the book into focus. The near point of the eye is the minimum distance of an object from the eye at which it produces a sharp image on the retina. This distance is also called the least distance of distinct vision (Fig.12.37). An object closer to the eye than the near point appears blurred. For people in their early twenties with normal vision, the near point is located about 25 cm from the eye. It increases to about 50 cm at the age 40 years and to roughly 500 cm at the of age 60 years. The far point of the eye is the maximum distance of a distant object from the eye on which the fully relaxed eye can focus. A person with normal eyesight can see objects very far away, such as the planets and stars, and thus has a far point located at infinity. Majority of people not have “normal eyes” in this sense! 12.16 DEFECTS OF VISION The inability of the eye to see the image of objects clearly is called defect of vision. The defects of vision arise when the eye lens is unable to accommodate effectively. The images formed are therefore blurred. Nearsightedness (myopia) Some people cannot see distant objects clearly without the aid of spectacles. This defect of vision is known as short sight or nearsightedness and it may be due to the eyeball b #humanEye #humaneye #10thphysics #accommodation #nearpoint #farpoint #10thclassphysics #class10 #urdu #hindi #10thPhysics #physics #lecture #freeOnlineClasses #matricPart2 #10th #videolecture #atifahmedofficial #atifahmadofficial