Laws; of Refraction. bends away from the normal. more dense medium bends towards the normal. to another does not bend. It is not

Transcription

1 Science 8 Laws; of Refraction 1. tight that moyes at an angle from a less dense medium to a more dense medium bends towards the normal. (The second medium slows the light down) Note: The angle of refraction, r, is always the angle between the hefracfed light ray and the normal. Air (less dense) Water (more dense) Angle of refraction (r) Normal 2. Light that moves at an angle from a more dense medium to a less dense medium bends away from the normal. (The second medium speeds the light up) Air (less dense) Water (more dense) Normal Light that moves straight on from one medium to another does not bend. It is not refracted. Air (less dense) r Light ray Water (more dense) 1 f r Norma!

2 Using Lenses io Form Images Textbook pages Before You Read Section 5.0 Summary Many common devices, such as eyeglasses and magnifying glasses, have lenses. What are lenses used for? Record your ideas in the lines below. Stofe the Main ideas As you read this section, stop after each paragraph. Put what you have just read into your own words. incoming light rays concave lens refiacted light rays are diverging What is a lens? A lens is a piece of transparent material that is curved so that light rays will refract as they pass through it. The more curved the sides of a lens are, the more a ray of light will refract as it passes through the lens. There are two types of lenses: concave and convex. What is a concave lens? Reading Chec/f 1. What happens to light rays that pass through a concave lens? A concave lens is thinner in the middle and thicker at the edges refracts light rays that pass through it away from the normal. The light rays diverge and do not meet at a focal point. forms images that are upright forms images that are smaller than the object 80 MHR Section 5.3 Using Lenses to Form Images 2006 McGraw-Hill Ryerson Limited

3 Section ew Summary What is a convex lens? A convex lens is thicker in the middle and thinner at the edges. 4 retracts light rays that pass through it toward the normal. The light rays converge at a focal point. The image formed by a convex lens depends on how far the object is from the focal point. The distance from the centre of the lens to the focal point is called the focal length. If an object is between the lens and the focal point (less than one focal length), the image is upright and larger than the object. If an object is more than one focal length away from the lens, the image is upside down and smaller than the object ^ continued OReading Check 2. What is the focal length of a lens? Distance of an object from the convex lens more than two focal lengths between one and two focal lengths directly at the focal point less than one focal length How the image compares with the object upside down and smaller upside down and larger no image forms upright and larger 2006 McGraw-Hili Ryerson Limited Section 5.3 Using Lenses to Form images MHR 81

4 Use with textbook pages Light rays and lenses 1. Will the image be (a) larger, smaller, or the same size as the object? upright or upside down? more than 2 focal lengths 2. Will the image be (a) larger, smaller, or the same size as the object? (b) upright or upside down? between 1 and 2 focal lengths 3. Will the image be (a) larger, smaller, or the same size as the object? (b) upright or upside down? between l and 2 focal lengths 4. Will the image be (a) larger, smaller, or the same size as the object? (b) upright or upside down? more than 2 focal lengths 82 MHR 8 Section 5.3 Using Lenses to Form images 2006 McGraw-Hill Ryerson Limited

5 Applying Knowledge Section Use with textbook pages Concave lenses and convex lenses Compare and contrast concave lenses and convex lenses. Draw the lens. Do light rays converge or diverge? Is the image upright or upside down? Is the image smaller or larger than the object? 2006 McGraw-Hill Ryerson Limited Section 5.3 Using Lenses to Form Images MHR 83

6 Vocabulary Section 5.3 Use with textbook pages Lenses puzzle Use the clues to help you solve the crossword puzzle Across 3. a concave lens refracts light rays the normal 5, mirror that curves outwards 6, if the object is more than two focai lengths from a convex iens, it will aooear to be 9. the focal is the distance frnm the centre of the lens to where light rays converge 13, light rays coming together 14. a concave lens Is in the middle Down 1, if the object is iess than one focai length from a convex iens, it will aooear to be uorioht and 2, liaht ravs meet at the focal 4. if the object is one or more focal lengths from a convex iens, it will aooear to be 7, a convex lens refracts liaht ravs the normal 8, images formed by concave lenses are always smaller and 10. a concave iens is attheedaes 11. light rays spreading apart 12. mirror that curves inward 84 MHR Section 5.3 Using Lenses to Form Images 2006 McGraw-Hill Ryerson Limited

7 Section 5.3 Use with textbook pages , 7. Which of the following is a concave lens? A. 1 G. Match the Term on the left with the best Descriptor on the right. Each Descriptor may be used only once. Term 1. lens 2. focal length 3. convex lens 4. concave lens Descriptor A. point where the converging light rays meet B. a piece of transparent material that bends light C. lens that is thinner in the middle than at the edge D. lens that is thicker in the middle than at the edge E. distance from the centre of the lens to the focal point Circle the Jetter of the best answer. 5. What happens to the light rays that pass through a convex lens? A. all the light rays diverge B. all the light rays converge C. all the light rays are absorbed by the lens D. some light rays diverge and some light rays converge 6. Describe the image that is produced by a concave lens. A. it is upright and larger than the object B. it is upright and smaller than the object C. it is upside down and larger than the object D. it is upside down and smaller than the object 8. A concave lens reflects light rays A. towards the normal B. away from the normal C. along the normal D. none of the above 9. A convex lens reflects light rays A. towards the normal B. away from the normal C. along the normal D. none of the above 10. Light rays converge A. at the focal length B. at the focal point G. inside the lens D. on the edge of the lens 11. If the object is more than two focal lengths from a convex lens, the image will be A. upside down and smaller B. upside down and larger C. upright and larger D. no image forms 2006 McGraw-Hill Ryerson Limited Section 5.3 Using Lenses to Form Images MHR 85

8 DATE: NAME: CLASS: Hif'ima. Goal Complete this page to show your understanding of how lenses bend light. What to Do Review pages of BC Science 8. Then answer these questions and complete the diagrams. 1. Describe a concave lens. 2. Light rays when passing through a concave lens. 3. Describe a convex lens. 4. Light rays when passing through a convex lens. 5. Sometimes people use the phrase double convex or double concave to describe a lens. They are referring to the shape of each surface. To identify concave and convex lenses, it is the thickness of the glass in the middle compared to the thickness at the edges that counts. Classify the following lenses as convex or concave. 6. Draw die paths of the light through each of the following lenses. Concave lens with small curve Concave lens with large curve Convex lens with small curve Convex lens with large curve Copyright 2006, McGraw-Hili Rycrson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved. This page may be reproduced for classroom use by die purchaser of this book without the written pemmriunof the publisher.