Elements of Physics Light and the Electromagnetic Spectrum Teacher s Guide

Transcription

1 Teacher s Guide Grade Level: 9 12 Curriculum Focus: Physical Science Lesson Duration: Three class periods Program Description One of the most fundamental forces in the universe, light has been one of the most difficult riddles to unravel. Examine the field of optics, and see how scientists came to understand refraction, reflection, and the behavior of light as it passes through lenses. Students will learn about James Clerk Maxwell's theory of electromagnetism, as well as how theoretical insights have led to electricity and telecommunications developments that have transformed our lives. Onscreen Questions How do lenses affect light? What are some common uses of electromagnetic waves? What electromagnetic waves are used to create and transmit television? What is a disadvantage of digital manipulation in television? Lesson Plan Student Objectives Predict what happens when light encounters an opaque substance. Predict what happens when light travels from one medium to another. Conduct an experiment that illustrates what happens when light encounters an opaque substance and when light travels from one medium to another. Summarize the results of the experiment and write a conclusion explaining how light behaves when it encounters an opaque substance and when it travels from one medium to another. Materials Elements of Physics: video Computer with Internet access Paper and pencils Five clear containers (one for each group)

2 Teacher s Guide 2 Water Five pencils (one for each group) Cooking oil Before the start of the class, decide how you would like to handle the distribution of materials for the investigation. One student from each group can come up to a central area to collect the materials, or you can hand out the materials to each group. Each group will need the following: A clear container Water One pencil Cooking oil Procedures 1. Begin the lesson by asking students to write down what happens in the following two scenarios: What happens when light encounters an opaque substance? What happens when light travels from one medium to another? After students make their predictions, have them put the sheets away until later in the lesson. 2. Tell students that they are going to work in small groups to find out how light behaves when it encounters an opaque substance and when it travels from one medium to another. Divide the class into five groups. Make sure that each group has the materials it needs. Then ask the groups to follow the directions below. Fill a clear container about three-fourths of the way with water. Look at the boundary between water and air from two different angles. First, look down at the boundary. Ask students to write down their observations. Hold the container up so that the boundary is below eye level. Ask students to write down their observations. Put a pencil into the container at an angle. Observe the top of the boundary. Ask students to write down their observations. Add a layer of cooking oil on top so that there are now two layers. Observe the boundary between the two layers when looking down and from eye level. Then observe what happens when a pencil is placed in the container. Ask students to write down their observations. 3. After students have completed the investigation, ask them to discuss their observations and write a set of conclusions from their group. If students would like additional background, suggest that they watch the segment Properties of Light, part of the video, Elements of Physics:.

3 Teacher s Guide 3 4. Have a class discussion about the results of the investigation. Make sure that students understand the following: When students look down at the boundary between water and air, they will notice that the surface looks like a mirror. That s because the light reflects, or bounces off, the surface of the water. When students hold up the container, the surface looks clear; reflection is taking place here as well. When students put the pencil in the container with water, they will notice it looks bent. That s because of refraction, which is what happens when light travels from one medium (the water) to another (air). When light travels from air to water, it slows down, making the pencil appear bent. The amount the light bends is called the index of refraction. When students add the layer of oil, the index of refraction is less than it was with just the layer of water. The pencil still looks bent, but not quite as much as when the container just held water. 5. During the next class period, go over these ideas again. Make sure that students understand the difference between reflection and refraction and what the index of refraction is. 6. Conclude the lesson by asking students to review the predictions they made before conducting the investigations. How have these ideas changed as a result of working on these materials? How would they explain reflection and refraction? Assessment Use the following three-point rubric to evaluate students' work during this lesson. 3 points: Students made sound predictions about the way light behaves when it hits an opaque substance and when it travels from one medium to another; worked well with their groups in conducting the investigation; synthesized their results in a logical way and wrote a complete, accurate summary explaining how light behaves when it hits an opaque substance and when it travels from one medium to another. 2 points: Students made reasonably sound predictions about the way light behaves when it hits an opaque substance and when it travels from one medium to another; worked satisfactorily with their groups in conducting the investigation; synthesized their results in a reasonably logical way and wrote a mostly complete and accurate summary explaining how light behaves when it hits an opaque substance and when it travels from one medium to another. 1 point: Students had difficulty making predictions about the way light behaves when it hits an opaque substance and when it travels from one medium to another; had difficulty working with their groups in conducting the investigation; and did not synthesize their results in a logical way or complete a summary explaining how light behaves when it hits an opaque substance and when it travels from one medium to another.

4 Teacher s Guide 4 Vocabulary angle of incidence Definition: The angle at which light strikes a surface Context: All electromagnetic waves, including light, microwaves, and X-rays, strike a surface at a unique angle of incidence. angle of reflection Definition: The angle at which light bounces off a surface Context: The law of reflection states that the angle of incidence always equals the angle of reflection. index of refraction Definition: A measure of how much light bends when it moves from one medium to another Context: Because glass refracts light more than air or water, the index of refraction is higher when light passes through this medium than when it passes through the other two. light Definition: A small part of the electromagnetic spectrum that travels in waves and enables us to see the world Context: Light, also referred to as visible light, is the part of the electromagnetic spectrum that we can see; it is made up of different wavelengths, each of which has a different color. reflection Definition: The bouncing back of light when it strikes an opaque surface through which it cannot pass Context: The reason you can see yourself in a mirror is because of reflection; the surface reflects all the light directed at it, so that you can see an image of yourself. refraction Definition: The bending of light due to a change in speed as it moves from one medium to another Context: When light travels through a prism, refraction takes place; each wavelength is refracted at slightly different angles, resulting in an array of colors called a rainbow.

5 Teacher s Guide 5 Academic Standards National Academy of Sciences The National Science Education Standards provide guidelines for teaching science as well as a coherent vision of what it means to be scientifically literate for students in grades K 12. To view the standards, visit this Web site: This lesson plan addresses the following national standards: Physical Science: Interactions of matter and energy Mid-continent Research for Education and Learning (McREL) McREL s Content Knowledge: A Compendium of Standards and Benchmarks for K 12 Education addresses 14 content areas. To view the standards and benchmarks, visit This lesson plan addresses the following national standards: Science: Physical Sciences Understands the sources and properties of energy Language Arts: Viewing Uses viewing skills and strategies to understand and interpret visual media; Writing: Uses the general skills and strategies of the writing process, Gathers and uses information for research purposes; Reading: Uses reading skills and strategies to understand and interpret a variety of informational texts DVD Content This program is available in an interactive DVD format. The following information and activities are specific to the DVD version. How to Use the DVD The DVD starting screen has the following options: Play Video This plays the video from start to finish. There are no programmed stops, except by using a remote control. With a computer, depending on the particular software player, a pause button is included with the other video controls. Video Index Here the video is divided into sections indicated by video thumbnail icons; brief descriptions are noted for each one. Watching all parts in sequence is similar to watching the video from start to finish. To play a particular segment, press Enter on the remote for TV playback; on a computer, click once to highlight a thumbnail and read the accompanying text description and click again to start the video. Curriculum Units These are specially edited video segments pulled from different sections of the video (see below). These nonlinear segments align with key ideas in the unit of instruction. They

6 Teacher s Guide 6 include onscreen pre- and post-viewing questions, reproduced below in this Teacher s Guide. Total running times for these segments are noted. To play a particular segment, press Enter on the TV remote or click once on the Curriculum Unit title on a computer. Standards Link Selecting this option displays a single screen that lists the national academic standards the video addresses. Teacher Resources This screen gives the technical support number and Web site address. Video Index I. The Nature of Light (4 min.) To understand light, we need to understand the electromagnetic spectrum. Explore questions about light and the electromagnetic spectrum that have baffled scientists throughout history. II. Properties of Light (4 min.) The physical properties of light allow us to see the world around us. Learn about the properties of light, and explore why we see what we see. III. Putting Electromagnetism to Work (4 min.) The energies found on the electromagnetic spectrum have many different uses. Explore an entire spectrum of energy and learn about the uses of radio waves, X-ray waves, and visible light. IV. The Wonder of Television (38 min.) Learn about the history and inner workings of analog and digital TV systems. Curriculum Units 1. The Basics of Electromagnetic Waves Q: What do you know about the electromagnetic spectrum? Q: How are electricity and magnetism related? A: Electromagnetic waves are a result of electric and magnetic fields. Electricity and magnetism

7 Teacher s Guide 7 result from the movement of electrons. When electrons move, they release energy in the form of electromagnetic waves. 2. Reflection, Refraction, and Light Q: How do you rely on visible light? Q: When do reflection and refraction occur, and what is an example of each? A: Reflection occurs when light encounters an opaque substance and bounces off it. A mirror reflects light. Refraction occurs when light travels through a transparent medium. Changing the substance through which light travels changes its speed and direction. One result of refraction is a distorted image. A prism refracts light. 3. Frequencies on the Electromagnetic Spectrum Q: What types of electromagnetic energy do you think are most useful and why? Q: How does ultraviolet, X-ray, and gamma radiation affect humans? A: As frequency increases, electromagnetic radiation becomes more dangerous to humans and other living creatures. Lower frequencies of ultraviolet light are less harmful, but overexposure to higher frequencies of UVB and UVC rays may cause skin cancer. X-rays have a higher frequency than ultraviolet rays; prolonged exposure is dangerous to humans. Gamma rays have the highest frequency of all electromagnetic energy. Gamma rays are extremely dangerous to humans and have no practical applications. 4. From the Racetrack to Your Television Set Q: What types of information do you get from watching television? Q: How do images from Daytona travel from the remote controlled camera to local TV stations? A: First, light images are turned into flowing electrons in the aerial camera. Next, electrons are

8 Teacher s Guide 8 transformed into microwaves, beamed from the tiny helicopter to a man holding an antenna on a pole. The waves are changed back to electrons and zapped down the wire to television sets in the director s booth. The signal is beamed up to a relay satellite and down to New York. In the network control room, commercials are added to the electronic stream. They return to space through another satellite link and are transmitted to local stations. 5. The Early History of Television Q: What do you think your life would be like without television? Q: Why is Philo Farnsworth known as the father of electronic television? A: Farnsworth created the image dissector, which was the first successful electronic pickup tube. He also built an electronic receiver and gave the first demonstrations of electronic television in the late 1920s. 6. The Modern Color Television System Q: Have you ever watched a black-and-white television? Q: What do the television terms field and frame mean? A: Television cameras have a ray gun at the back of the picture tube that fires a thin beam to light up a dot on the screen. When the beam is scanning left to right, the dot leaves behind a glowing line. The lines merge to form a picture. Modern televisions have dots that scan more than 500 lines. Each time the dot scans the whole screen, it makes one picture and snaps back. Engineers call these fields. Two fields merge together to create a whole picture that engineers call a frame. TVs in North America and Japan have 30 frames per second. 7. Advances in Video Recording Q: What is your favorite genre of television?

9 Teacher s Guide 9 Q: What were some issues with early television production recording machines? A: Early television recording machines were bulky, very expensive, and often had technical problems. Four record heads mounted on a disc screened at 14,400 rpm. It required 32 passes for the video heads to complete one picture. If the machines were not constantly monitored and adjusted during playback, segments of the recording picture would not match. It was impossible to play back slow motion and still frames. 8. Analog vs. Digital Television Q: What are some common uses of digital technology? Q: What are some advantages of digital video? A: Digital video offers pristine pictures and transmits information more efficiently. It creates space on the cable for more TV channels. With digital video, pictures can be manipulated in new ways.