Lesson Lesson3 3 Essential Question How Do Lenses Essential Question How Do Lenses and Mirrors Objectives • Compare how plane, and Mirrors Affect convex, and concave Affect Light? mirrors refl ect light. Light? • State the law of What refl ective surfaces do you see in your classroom? refl ection. Preview Lesson Content What are the different properties of these surfaces that • Compare refraction Mirrors by concave and Read the objectives with students and help make some refl ections better than others? are convex lenses. very smooth surfaces usually made of polished metal them pronounce each term in the vocabulary • Compare how or silver-coated glass. People have used mirrors for optical devices are list. Then, ask students to name diff erent ways thousands of years. When the Israelites were constructing used. they have used mirrors and lenses. the tabernacle, the bronze basin and stand were made Vocabulary from the bronze mirrors donated by the women. What is another use of mirrors in history? mirror law of refl ection Explain Mirrors Explain virtual image Mirrors come in a variety of types. Some mirrors have a concave Mirrors fl at surface while others have a curved surface. Where might focus you fi nd fl at mirrors in your home? Where have you seen real image curved mirrors used? Why were they used there? Whether focal length Objectives a mirror is fl at or curved, the law of refl ection states that convex light refl ects off the mirror in straight lines at the same angle • Compare how plane, convex, and concave as the light hits the mirror. This means the incoming angle, mirrors refl ect light. called the angle of incidence, equals the angle at which the refl ected ray leaves, called the angle of refl ection. • State the law of refl ection. Normal A line drawn perpendicular to the surface of the mirror called Set Goals the normal, labeled Normal in this diagram, divides the angle As they study this lesson, ask students to formed between the incident ray summarize what they have learned in their and the refl ected ray into two own words. Incident ray Reflected ray equal angles. Use a protractor. What is the Develop Key Vocabulary angle of incidence in the picture? mirror Explain to students that mirrors refl ect 407 images. law of refl ection When discussing the law of refl ection, the incoming ray is called the incident ray. The returning ray is called the KH_BD1_SEG5_U4C12L3_407-415.indd 407 6/22/13 11:28 AM Science Background refl ected ray. Understand Visuals Concave Mirrors in Telescopes Every satellite dish you see on people’s roofs is a concave mirror for electromagnetic waves. Concave mirrors can Walk students through the diagram of focus electromagnetic waves other than light. A radio telescope uses a light refl ecting off of a plane mirror. Ensure concave mirror made of wire mesh to focus incoming parallel radio waves to students are clear that a plane mirror is the a point. The mirror telescope focuses radio waves onto a receiver suspended fl at kind of mirror they are most familiar with. at the focus. The telescope detects faint radio waves from distant objects Which of the pictured angles does the law in the universe. The giant radio telescope at Arecibo, Puerto Rico, is the of refl ection describe? the angles formed largest in the world. Its concave mirror is 305 m (1000-ft) across. China has between the normal and the light rays started construction on an even larger 500-m (1640-ft) radio telescope. Its Use a protractor. What is the angle construction is expected to be completed in 2016. of incidence in the picture? The ray is bisecting a right angle, so the angle of incidence is 45 degrees. Chapter 12 • Lesson 3 407 KKH_BD1_TEG5_U4C12L3_407-415.inddH_BD1_TEG5_U4C12L3_407-415.indd 407407 66/24/13/24/13 11:21:21 PMPM Lesson Activity Locate diff erent everyday objects with fl at or curved Explain (cont.) refl ective surfaces, like spoons. Examine how each object acts as a mirror. Experiment with refl ecting light off each Lesson Activity object, using sunlight, a penlight fl ashlight, or other light sources. How did the diff erent refl ective surfaces How did the diff erent refl ective surfaces aff ect the aff ect the object’s image? Were they object’s image? Were they distorted or changed in distorted or changed in some way? some way? Explain. Explain. Sample answer: Pretty much any polished surface will refl ect light. My Plane Mirrors refl ection was upside down when I looked Plane mirrors are fl at mirrors that refl ect light. In Bible at the inside of a spoon, because it is curved times, they were made of polished metal. Today, they are and bowl-shaped. As I got closer, I could more commonly made of glass or plastic coated with a thin fi lm of metal. The image produced by a plane mirror that even fl ip the refl ection. Sometimes the appears “behind” it is called a virtual image. A virtual image image was bigger, sometimes smaller. In is one that forms where light cannot actually reach. The other round objects, such as a doorknob, image appears to be as far behind the mirror as the object is the refl ection was bent. in front of the mirror. What does an image look like in a plane mirror? How is Develop Key Vocabulary the image different from the actual object? Use a plane mirror to look at this line of text. What does the text look like in virtual image Point out the kinship between the mirror? the fi rst part of this compound word and the term virtual reality. It means something Explore-a-Lab that “does not physically exist, but is made Structured Inquiry to appear as if it does. “ Explain that a virtual How does the image of your face appear in diff erent image is one that forms where light rays cannot Scripture mirrors? Spotlight actually go. Work with a partner. Observe the image of your face in a Probably the most plane mirror, a concave mirror, and a convex mirror. Hold famous verse in each mirror about 25 cm (10 in.) from your face. Have your Scripture Spotlight the Bible that partner move the mirror. Then switch places. Use a table, like 1 Corinthians 13:12. What type of mirror do mentions a mirror is the one below, to record the data. 1 Corinthians 13:12. you think is being referred to in this verse— Type of Image right Larger, Eff ect of Eff ect of What type of mirror mirror side up or smaller, or the moving mirror moving mirror plane, convex, or concave? Sample answer: do you think is being upside down? same size? closer? farther away? probably a plane mirror referred to in this Plane verse—plane, convex, Concave or concave? Explore-a-Lab Structured Inquiry Convex Make sure a set of concave and convex mirrors 408 is provided for each student group. If you do not have curved mirrors available, shiny metal soup or serving spoons could be substituted. KH_BD1_SEG5_U4C12L3_407-415.indd 408 6/19/13 10:33 AM However, students may not be able to get a clear, Science and Technology larger, right-side-up image to form when they move the concave side closer to themselves. Mirrors and Photography The single lens refl ex (SLR) camera is popular How does the image of your face appear with amateur photographers. This type of camera has a mirror behind the in diff erent mirrors? Plane mirror: right lens. The mirror allows the photographer to see the same image that will side up, same size, but reversed right to be recorded on fi lm or digitally. When you depress the shutter release, the left, image gets bigger, image gets smaller; mirror fl ips out of the way and the shutter opens, exposing fi lm to the light concave mirror: upside down, smaller, or digitally recording the image on a memory card. image gets larger and right side up, image is upside down and smaller; convex mirror: right side up, smaller, image gets larger, image gets smaller. 408 Chapter 12 • Lesson 3 KKH_BD1_TEG5_U4C12L3_407-415.inddH_BD1_TEG5_U4C12L3_407-415.indd 408408 66/19/13/19/13 33:14:14 PMPM ien Sc ce StructuredS Inquiry Record your work for this inquiry.. Your teacher may also assign the Discover J l related Guided Inquiry. ourna Discover Looking at Lenses Materials How do lenses aff ect light as it • 2 convex lenses (labeled A Use the inquiry activities as an opportunity for passes through them? and B) students to perform hands-on investigations • 2 concave lenses (labeled C and thinkthin like a scientist. Procedure and D) • white poster board 1. Open a book to a page that has both text and • meterstick StructuredS Inquiry pictures. Stand the book upright at least 1.5 m • book with text and one or (about 60 in.) from your eyes. Hold a convex more pictures lens at arm’s length and observe the page Lookingk at Lenses through the lens. Note the size (larger or smaller) and positioni (upright or upside down). Record your observations. How do lenses aff ect light as it 2. Observe any changes to the image as you move the lens to the passes through them? following distances from the book: 100 cm (39 in.), 75 cm (30 in.), Preparation and Tips 50 cm (20 in.), 25 cm (10 in.), 10 cm (4 in.), and 5 cm (2 in.) closer to the book.