logging in or signing up maths of class 9th student.sandeep_7 Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: Embed: Flash iPad Copy Does not support media & animations WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 9095 Category: Education License: All Rights Reserved Like it (5) Dislike it (2) Added: July 05, 2010 This Presentation is Public Favorites: 0 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Slide 1: welcome to our presentation... Slide 2: PHYSICS PRESENTATION sandeep.. $ sourav.. are presenting...... Slide 3: structure of the human eye Slide 4: The eyes are undoubtedly the most sensitive and delicate organs we possess, and perhaps the most amazing. They present us with the window through which we view the world, and are responsible for four fifths of all the information our brain receives – which is probably why we rely on our eyesight more than any other sense. EYE Slide 5: The images we see are made up of light reflected from the objects we look at. This light enters the eye through the cornea. Because this part of the eye is curved, it bends the light, creating an upside-down image on the retina (this is eventually put the right way up by the brain). Focusing on a nearby object Focusing on a distant object Slide 6: What happens ....... when light .... reaches the retina? Slide 7: The retina is a complex part of the eye, but only the very back of it is light-sensitive. This part of the retina has roughly the area of a 10p coin, and is packed with photosensitive cells called rods and cones. These allow us to see images in colour and detail, and to see at night. Slide 8: Cones are the cells responsible for daylight vision. There are three kinds - each responding to a different wavelength of light: red, green and blue. The cones allow us to see in colour and detail. Rods are responsible for night vision. They are sensitive to light but not to colour. In darkness, the cones do not function at all. Slide 9: how ..? the image send to ........... brain Slide 10: Once the image is clearly focused on the sensitive part of the retina, energy in the light that makes up that image creates an electrical signal. Nerve impulses can then carry information about that image to the brain through the optic nerve. Slide 11: common some diseases eye Slide 12: 1. Short sight (myopia) and long sight (hypermetropia) are common conditions, both caused by the cornea and lens not focusing properly on the retina.Short sight is where the eyeball is elongated or the lens is too thick, causing the image to focus in front of the retina. Common eye problems 2.Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina 3.Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina : 2.Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina 3.Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina Slide 14: 4.There are other sight-threatening conditions which are not so easily corrected or overcome. Cataract, trachoma, glaucoma and river blindness , for example, will cause complete blindness if left untreated. Sightsavers is preventing and curing these diseases and restoring sight where possible. Slide 15: how...?? we can protect our eye Slide 16: Many people believe that vision loss is a normal part of aging. But it doesn't have to be so. There are things that you can do to reduce your risk of vision loss. From wearing sunglasses and eating leafy greens, to managing diabetes in a responsible manner, there are a number of ways to preserve your sight. people's view Slide 17: Embarrassing, but true—when we go to the beach, we worry about shark attacks, sting rays, and tsunamis. When we’re hiking or skiing, we fret about avalanches and mountain lions. In fact, true threats are often much less dramatic but all the more real. A day on the water or in the mountains should have us more concerned about sun damage than about wild animals or natural disasters. Sun Damage Prevention Slide 18: 2. Eye disorders and cancers related to excessive sunlight exposure occur most frequently among older people and in those with fair skin and light-colored (blue or green) eyes. However, these conditions can and do occur in all kinds of people. Slide 19: 3.Ultraviolet (UV) radiation is simply energy of a particular wavelength that spreads out (radiates) from its source—in this case, the sun—the way the spokes of a wheel radiate from the hub. The sun’s electromagnetic energy consists of UVA, UVB, and UVC rays. Short-wavelength UVC rays are blocked by the ozone layer that envelops the Earth. Slide 20: enjoy.. OR .not bye.. bye.. ........go class.. very funny sandeep.. what......? sourav what. You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.