Exploring Mirrors and Lenses: Reflections and Refractions of Light, Exams of Law

Download Exploring Mirrors and Lenses: Reflections and Refractions of Light and more Exams Law in PDF only on Docsity! Incident ray Normal Reflected ray Essential Question How Do Lenses and Mirrors Affect Light? What refl ective surfaces do you see in your classroom? What are the different properties of these surfaces that make some refl ections better than others? Mirrors are very smooth surfaces usually made of polished metal or silver-coated glass. People have used mirrors for thousands of years. When the Israelites were constructing the tabernacle, the bronze basin and stand were made from the bronze mirrors donated by the women. What is another use of mirrors in history? Mirrors Explain Mirrors come in a variety of types. Some mirrors have a fl at surface while others have a curved surface. Where might you fi nd fl at mirrors in your home? Where have you seen curved mirrors used? Why were they used there? Whether a mirror is fl at or curved, the law of refl ection states that light refl ects off the mirror in straight lines at the same angle as the light hits the mirror. This means the incoming angle, called the angle of incidence, equals the angle at which the refl ected ray leaves, called the angle of refl ection. Objectives • Compare how plane, convex, and concave mirrors refl ect light. • State the law of refl ection. • Compare refraction by concave and convex lenses. • Compare how optical devices are used. Vocabulary mirror law of refl ection virtual image concave focus real image focal length convex 3Lesson A line drawn perpendicular to the surface of the mirror called the normal, labeled Normal in this diagram, divides the angle formed between the incident ray and the refl ected ray into two equal angles. Use a protractor. What is the angle of incidence in the picture? 407 KH_BD1_SEG5_U4C12L3_407-415.indd 407 6/22/13 11:28 AM Plane Mirrors Plane mirrors are fl at mirrors that refl ect light. In Bible times, they were made of polished metal. Today, they are more commonly made of glass or plastic coated with a thin fi lm of metal. The image produced by a plane mirror that appears “behind” it is called a virtual image. A virtual image is one that forms where light cannot actually reach. The image appears to be as far behind the mirror as the object is in front of the mirror. What does an image look like in a plane mirror? How is 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 the mirror? Scripture Spotlight Probably the most famous verse in the Bible that mentions a mirror is 1 Corinthians 13:12. What type of mirror do you think is being referred to in this verse—plane, convex, or concave? Structured Inquiry How does the image of your face appear in diff erent mirrors? Work with a partner. Observe the image of your face in a plane mirror, a concave mirror, and a convex mirror. Hold each mirror about 25 cm (10 in.) from your face. Have your partner move the mirror. Then switch places. Use a table, like the one below, to record the data. Explore-a-Lab Type of mirror Image right side up or upside down? Larger, smaller, or the same size? Eff ect of moving mirror closer? Eff ect of moving mirror farther away? Plane Concave Convex Locate diff erent everyday objects with fl at or curved refl ective surfaces, like spoons. Examine how each object acts as a mirror. Experiment with refl ecting light off each object, using sunlight, a penlight fl ashlight, or other light sources. How did the diff erent refl ective surfaces aff ect the object’s image? Were they distorted or changed in some way? Explain. Lesson Activity 408 KH_BD1_SEG5_U4C12L3_407-415.indd 408 6/19/13 10:33 AM Convex Mirrors A convex mirror is curved like the back of a spoon. The edges of the mirror curve away from you. A convex mirror makes refl ected light rays spread out. The green lines in the convex mirror diagram are where the refl ected rays are traced backwards. They seem to come to a point behind the mirror, forming a smaller, virtual image. Convex mirrors are used on vehicles as the side-view mirrors to help drivers have a wider view of surrounding cars to the side and at the back of the vehicle. What are other uses for a convex mirror? Check for Understanding Compare and contrast the three types of mirrors. Scripture Spotlight Read James 1:23. What does James say someone is like who listens to God’s word but does not do what it says? What is he trying to tell us? Fun house or carnival mirrors combine concave and convex mirror shapes to distort images in amusing ways. What kind of image distortions are produced by convex or concave shapes in a fun house mirror? 411 KH_BD1_SEG5_U4C12L3_407-415.indd 411 6/19/13 10:33 AM Lenses Explain Lenses offer a way to refract light waves for many different uses. Lenses are smooth, curved pieces of transparent glass or plastic. They are made to cause light rays to form certain kinds of images. What are some objects that use lenses? What are the lenses being used for in these objects? Why do lenses work the way they do? Recall what you learned about light in Lesson 1. • Light always travels in straight lines. • Light travels more slowly through glass or plastic than air. • Light bends when it moves from one substance to another. The amount of bending depends on how the lens is curved and the type of material that the lens is made from. Lenses can have one or two curved surfaces, like mirrors. Lenses are grouped by shape into two kinds—convex and concave. Convex Lenses Look at the illustration on the next page. You will see that convex lenses are thicker in the middle than at the edges. A thicker convex lens will bend light more than a thinner, less curved lens. The diagram shows how a convex lens refracts light rays. The rays are bent so they come together at a point behind the lens—the focus. A convex lens that is thicker and more curved has a shorter focal length than one that is thinner and less curved. How might a convex lens be useful? Concave Lenses Concave lenses are thinner in the middle than at the edges. The diagram shows how a concave lens refracts light rays. Notice that the light rays do not come together at a focus. Instead, the rays are bent and spread apart as they pass through the lens. How might a concave lens be useful? There is an easy way to remember how light rays travel through lenses. Light rays passing through a lens always bend toward the thickest part of the lens. Light waves bend toward the thick center in a convex lens.They bend out toward the thick edge in a concave lens. 412 KH_BD1_SEG5_U4C12L3_407-415.indd 412 6/19/13 10:33 AM Focal point Focal point Because it can focus light, a convex lens can form a real image. A concave lens cannot form a real image because it cannot focus light. What type of lens would work best to help a person who has trouble seeing small words in a newspaper? Refraction of light through a convex lens Refraction of light through a concave lens Check for Understanding Think about the images you observed in the Structured Inquiry. How do you explain the images that appeared upside down? 413 KH_BD1_SEG5_U4C12L3_407-415.indd 413 6/19/13 10:33 AM