VIEWS: 14 PAGES: 35 POSTED ON: 4/8/2011
Grade 8 Science Unit 2: Optics Chapter 6: Lenses refract light to form images. Lenses A curved piece of transparent material that refracts light in a predictable way. Usually made from glass or plastic. Lenses There are two types of lenses: 1. Convex Centre of the lens bulges out Causes light rays to bend toward each other (converge) 2. Concave Centre of the lens is curved in Causes light rays to bend away from each other (diverge) Convex vs. Concave Lenses Convex Lenses Can act as a magnifying glass Each lens has its own focal length (the distance from the centre of the lens to the focal point) The greater the curvature of the lens, the shorter the focal length. (pg. 217) Lenses have focal points on either side because light shines through either side. The line through the centre of the lens is called the principle axis. Optical centre is where the principle axis meets the lens centre. Optical Centre Principle Axis Concave Lenses To find the focal point, you must extend the refracted rays back. Lenses with the greater curvature have the shortest focal length. (pg. 221) Corrective Lenses The Eye (pg. 229) Vision Near-sighted Vision See objects up close but not at a distance. Concave lenses are used to correct this vision. Near- sighted Vision Far-sighted Vision See objects at a distance but not up close. Convex lenses are used to correct this vision. Far-sighted Vision Determining Focal Length... You must include the following incident rays: 1. Travelling parallel to the p.a. 2. Travelling through the o.c. 3. Travelling through the F. Ray Diagrams: Convex Lenses Object between the lens and focal point. Object is between the focal point and 2X the focal length. Object is more than 2X the focal length. Ray Diagrams: Concave Lenses The above is true for an object in all positions. CORE STSE: “Fibre Optics” Fibre Cable Optical Technologies... 1. Microscopes Uses two convex lenses with relatively short focal points to magnify Magnified twice to increase enlargement The Microscope 2. Telescopes The objective lens has a longer focal length than the microscope. Can have either a refracting or reflecting telescope Refracting Telescope (pg. 245) The lenses bend light to focus it. The objective lens must be as large as possible to view distant galaxies (makes it heavy) Reflecting Telescope (pg. 246) Uses a concave mirror, plane mirror and a convex lens to collect and focus light from objects at a great distance. Most large telescopes are this type. The Hubble Space Telescope Launched in 1990 The Reflecting Telescope 3. Cameras (pg. 248) 4. Binoculars (pg. 247) 5. Face shields 6. Magnifying glasses 7. Contact lenses 8. Flashlights 9. Eye glasses The Nature of Science The development of new technologies involve many individuals and groups of people. These technologies can alter what we know about the nature of science. Individuals... 1602 Galileo 1672 Newton Groups...
Pages to are hidden for
"8 Unit 2 NEW Chapter 6"Please download to view full document