* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Mirrors form images by reflecting light.
Nonlinear optics wikipedia , lookup
Optical coherence tomography wikipedia , lookup
Diffraction grating wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Surface plasmon resonance microscopy wikipedia , lookup
Ultraviolet–visible spectroscopy wikipedia , lookup
Thomas Young (scientist) wikipedia , lookup
Optical flat wikipedia , lookup
Night vision device wikipedia , lookup
Ray tracing (graphics) wikipedia , lookup
Interferometry wikipedia , lookup
Optical aberration wikipedia , lookup
Chinese sun and moon mirrors wikipedia , lookup
Magic Mirror (Snow White) wikipedia , lookup
Nonimaging optics wikipedia , lookup
Atmospheric optics wikipedia , lookup
Harold Hopkins (physicist) wikipedia , lookup
Page 1 of 5 KEY CONCEPT Mirrors form images by reflecting light. BEFORE, you learned NOW, you will learn • EM waves interact with materials • Light can be reflected • About the science of optics • How light is reflected • How mirrors form images VOCABULARY EXPLORE Reflection optics p. 593 law of reflection p. 594 regular reflection p. 594 diffuse reflection p. 594 image p. 595 convex p. 596 concave p. 596 focal point p. 597 How does surface affect reflection? PROCEDURE 1 Tear off a square sheet of aluminum foil. Look at your reflection in the shiny side of the foil. MATERIALS aluminum foil 2 Turn the foil over and look at your reflection in the dull side. 3 Crumple up the piece of foil, then smooth it out again, shiny side up. Again, look at your reflection in the foil. WHAT DO YOU THINK? • How did the three reflections differ from one another? • What might explain these differences? Optics is the science of light and vision. COMBINATION NOTES Don’t forget to include sketches of important concepts in your notebook. Optics (AHP-tihks) is the study of visible light and the ways in which visible light interacts with the eye to produce vision. Optics is also the application of knowledge about visible light to develop tools—such as eyeglasses, mirrors, magnifying lenses, cameras, and lasers—that extend vision or that use light in other ways. Mirrors, lenses, and other optical inventions are called optical tools. By combining optical tools, inventors have developed powerful instruments to extend human vision. For example, the microscope uses a combination of mirrors and lenses to make very small structures visible. Telescopes combine optical tools to extend vision far into space. As you will see, some of the latest optical technology—lasers— use visible light in ways that do not involve human vision at all. Chapter 18: Light and Optics 593 Page 2 of 5 Mirrors use regular reflection. You have read that when light waves strike an object, they either pass through it or they bounce off its surface. Objects are made visible by light waves, or rays, bouncing off their surfaces. In section 3 you will see how the light waves create images inside the human eye. Light rays bounce off objects in a very predictable way. For example, look at the diagram on the left below. Light rays from a flashlight strike a mirror at an angle of 60° as measured from the normal, an imaginary line perpendicular to the surface of the mirror. This angle is called the angle of incidence. The angle at which the rays reflect off the mirror, called the angle of reflection, is also 60° as measured from the normal. The example illustrates the law of reflection, which states that the angle of reflection equals the angle of incidence. As you can see in the second diagram, holding the flashlight at a different angle changes both the angle of incidence and the angle of reflection. However, the two angles remain equal. normal angle of incidence 60º angle of reflection 60º 40º 40º The angle of reflection equals the angle of incidence. If the surface of an object is very smooth, like a mirror, light rays that come from the same direction will bounce off in the same new direction. The reflection of parallel light rays all in the same direction is called regular reflection. The light rays striking the mirror bounce back by regular reflection. Rays striking everything else bounce back by diffuse reflection. 594 Unit 4: Waves, Sound, and Light If the surface is not very smooth—even if it feels smooth to the touch, like a piece of paper—light rays striking it from the same direction bounce off in many new directions. Each light ray follows the law of reflection, but rays coming from the same direction bounce off different bumps and hollows of the irregular surface. The reflection of parallel light rays in many different directions is called diffuse reflection. Page 3 of 5 The Law of Reflection SKILL FOCUS How can you use mirrors to see around a corner? Analyzing PROCEDURE 1 To make a periscope, cut two flaps on opposite sides of the carton, one from the top and one from the bottom, as shown in the illustration. MATERIALS • paper milk or juice carton • scissors • tape • 2 mirrors slightly smaller than the bottom of the carton • protractor 2 Fold each flap inward until it is at a 45-degree angle to the side cuts and tape it into place. 3 Attach a mirror to the outside surface of each of the flaps. 4 Holding the periscope straight up, look through one of the openings. Observe what you can see through the other opening. WHAT DO YOU THINK? TIME 30 minutes mirror • Where are the objects you see when you look through the periscope? • How does the angle of the mirrors affect the path of light through the periscope? flap 1 tape flap 2 fold cut CHALLENGE How would it affect what you see through 45° the periscope if you changed the angle of the mirrors from 45 degrees to 30 degrees? Try it. step 1 Shape determines how mirrors form images. When you look in a mirror, you see an image of yourself. An image is a picture of an object formed by waves of light. The image of yourself is formed by light waves reflecting off you, onto the mirror, and back toward your eyes. Mirrors of different shapes can produce images that are distorted in certain ways. VISUALIZATION CLASSZONE.COM See reflection in action. Flat Mirrors Your image in a flat mirror looks exactly like you. It appears to be the same size as you, and it’s wearing the same clothes. However, if you raise your right hand, the image of yourself in the mirror will appear to raise its left hand. That is because you see the image as a person standing facing you. In fact, your right hand is reflected on the right side of the image, and your left on the left side. Check Your Reading If you wink your left eye while looking in the mirror, which eye in the image of you will wink? Chapter 18: Light and Optics 595 Page 4 of 5 The solid line shows the actual path of light. The broken line shows where the light appears to be coming from. If you look closely at your image in a mirror, you will notice that it actually appears to be on the far side of the mirror, exactly as far from the mirror as you are. This is a trick of light. The solid yellow arrows in the photograph above show the path of the light rays from the boy’s elbow to the mirror and back to his eyes. The light rays reflect off the mirror. The broken line shows the apparent path of the light rays. They appear to his eyes to be coming through the mirror from a spot behind it. VOCABULARY Try making sketches to help you remember the new terms on this page. Concave and Convex Mirrors Unlike light rays hitting a flat mirror, parallel light rays reflecting off a curved mirror do not move in the same direction. A convex mirror is curved outward, like the bottom of a spoon. In a convex mirror, parallel light rays move away from each other, as you can see in the diagram below on the left. A concave mirror is curved inward toward the center, like the inside of a spoon. Parallel light rays reflecting off a concave mirror move toward each other, as shown on the right. Convex Mirror Concave Mirror focal point light rays 596 Unit 4: Waves, Sound, and Light Page 5 of 5 The rays striking a concave mirror cross and then move apart again. The point at which the rays meet is called the focal point of the mirror. The distance between the mirror and its focal point depends on the shape of the curve. The images formed in these mirrors depend on the curve of the mirror’s surface and the distance of the object from the mirror. Your image in a curved mirror may appear larger or smaller than you are, and it may even be upside down. Convex Mirror Concave Mirror, Far Away Concave Mirror, Up Close Your image in a convex mirror appears smaller than you. If you are standing far away, your image in a concave mirror appears upside down and smaller than you. If you are standing inside the focal point, your image in a concave mirror appears right-side up and larger. All rays parallel to a line through the center of the mirror are reflected off the mirror and pass through the mirror’s focal point. Rays from the top of the object are reflected downward and those from the bottom are reflected upward. Check Your Reading How does your distance from the mirror affect the way your image appears in a concave mirror? KEY CONCEPTS CRITICAL THINKING 1. Explain the term optics in your own words. 4. Infer Imagine seeing your reflection in a polished table top. The image is blurry and hard to recognize. What can you tell about the surface of the table from your observations? 2. How is diffuse reflection similar to regular reflection? How is it different? 3. Describe the path that light rays take when they form an image of your smile when you look into a flat mirror. 5. Analyze Why do images formed by concave mirrors sometimes appear upside down? CHALLENGE 6. Synthesize Draw the letter R below as it would appear if you held the book up to (a) a flat mirror and (b) a convex mirror. R Chapter 18: Light and Optics 597