CHAPTER 15 Instruction and Intervention Support Interference and Diffraction 1 Core Instruction Chapter Resources ■ The Teacher’s Edition wrap has extensive teaching support for every lesson, including Misconception Alerts, Teach from Visuals, Demonstrations, Teaching Tips, Differentiated Instruction, and Problem Solving. ■ Several additional presentation tools are available online for every chapter, including Animated Physics features, Interactive Whiteboard activities, and Visual Concepts. Labs and Demonstrations Section Instruction Go Online for Materials Lists and Solutions Lists. ■ Textbook: Interference ■ Demonstrations: Interference in Sound Waves • Interference 15.1 Animated Physics: Diffraction in a Ripple Tank • How Distance Traveled Affects Interference • Visual Concepts: Combining Light Waves • Thin-Film Interference Interference Arising from Two Slits ■ Lab: Double-Slit Interference (Open Inquiry) Teaching Visuals: Conditions for Interference of Light Waves • Comparison of Waves in Phase and 180˚ out of Phase • Path Difference for Light Waves from Two Slits • Position of Higher-Order Interference Fringes PowerPresentations ■ Textbook: Diffraction ■ Demonstrations: Waves Bending Around Corners • Diffraction 15.2 Visual Concepts: Diffraction • Maxima and Minima in and Interference by a Single Slit • Light Diffraction by an Diffraction Patterns • Function of a Spectrometer Obstacle: Poisson Spot • Effect of Slit Size on Diffraction Teaching Visuals: Diffraction of Light with Decreasing Patterns • Multiple-Slit Diffraction Slit Width • Constructive Interference by a ■ Lab: Diffraction (Core Skill) Diffraction Grating • Function and Use of a Diffraction Grating in a Spectrometer • and more PowerPresentations ■ Textbook: Lasers ■ Demonstrations: Dancing Light • Interference in Laser Light 15.3 Visual Concepts: Comparing Noncoherent and Coherent Light • Laser • Function of a Compact Disc • Comparing Digital and Analog Signals • and more Teaching Visuals: Operation of a Laser • Components of a Compact Disc Player • Wave Fronts from Noncoherent and Coherent Light Sources PowerPresentations 516A Chapter 15 PREMIUM Content Find all of your resources online at HMDScience.com. 2 Support and Intervention 3 Specialized Support ■ Study Guide ■ Chapter Summary Audio Files Concept Maps ■ Differentiated Instruction: Inclusion, Below Level, and ■ Scientific Reasoning Skill Builder English Learners (TE wrap) Interactive Demos Sample Problem Set I Sample Problem Set II Where do I find it? PRINT DVD ONLINE Enrichment and Challenge Animated Physics ■ ■ Demonstrations (TE wrap) ■ ■ ■ Differentiated Instruction: Pre-AP (TE wrap) Labs ■ ■ ■ Why It Matters (STEM): Digital Video Players (SE) PowerPresentations ■ ■ ■ Careers in Physics: Laser Surgeon (SE) QuickLabs ■ ■ ■ Teaching Visuals ■ ■ Textbook ■ ■ ■ Visual Concepts ■ ■ Interactive Demos ■ ■ Concept Maps ■ ■ Sample Problem Set I ■ ■ Sample Problem Set II ■ ■ Scientific Reasoning Skill Builder ■ ■ Assessment Study Guide ■ ■ ■ Section Quizzes Chapter Summary Audio Files ■ ■ ■ Chapter Tests A and B Differentiated Instruction (TE wrap) ■ ■ Alternative Assessment (SE) Online Assessment and Remediation ■ ExamView Banks Interference and Diffraction 516B CHAPTER 15 The streaks of colored light you see coming from a compact disc resemble the colors that appear when white light passes through a prism. However, the compact disc Chapter Overview does not separate light by means of refraction. Instead, the light Section 1 identifies the conditions waves undergo interference. required for interference to occur and shows how to calculate the location of bright and dark fringes in double- slit interference. Section 2 describes how diffracted light waves interfere, shows how to calculate the position of fringes produced by a diffraction grating, and discusses the resolving power of optical instruments. Section 3 describes how a laser produces coherent light and explores applications of lasers. C15CHO002a About the Image The colors visible on the discs’ surfaces are characteristic of the light used in the photograph. Have students verify the ability of a compact disc to separate light into its particular spectrum by reflecting light from different sources off a compact disc’s surface. For example, sunlight is separated into all of the visible colors, while most fluorescent lighting produces only a few colors. ©Andrew Douglas/Masterfile (br) ©Don Farrall/Photodisc/Getty Images Lab 516Preview The following investigations support the Thin-Film Interference Untitled-295concepts 516 presented in this chapter. Waves Bending Around Corners 5/20/2011 7:54:11 AM LAB Diffraction and Interference by a Single Slit Diffraction (Core Skill) Light Diffraction by an Obstacle: Poisson Spot Double-Slit Interference (Open Inquiry) Effect of Slit Size on Diffraction Patterns Multiple-Slit Diffraction DEMONSTRATIONS Dancing Light Interference in Sound Waves Interference in Laser Light Interference in a Ripple Tank How Distance Traveled Affects Interference 516 Chapter 15 CHAPTER 15 Interference Focus and Motivate Activate Prior Knowledge and Diffraction KNowlEDGE TO REVIEW • The superposition principle: When two SECTION 1 mechanical waves pass through the Interference same space at the same time, their SECTION 2 displacements at each point add. Diffraction • When two waves with the same SECTION 3 frequency and amplitude overlap, the Lasers resulting wave has the same frequency as the individual waves. If the waves Why It Matters are in phase, the resultant wave has Devices called diffraction twice their amplitude. If they are 180° gratings use the principle of interference to separate out of phase, the amplitudes cancel. light into its component wavelengths. Diffraction ITEMS TO PROBE gratings are used in • Preconceptions about waves: Ask instruments called spectrometers, which are students what happens when two used to study the waves (A and B) travel toward each chemical composition and temperature of stars. other on a string and meet at a point where A’s displacement is 4 cm up and B’s displacement is 3 cm up. The displacement at that point is 7 cm up. What if A is 4 cm up and B is 3 cm ONLINE Physics down? The displacement is 1 cm up. HMDScience.com ONLINE LAB Diffraction PREMIUM Double-Slit Interference CONTENT Physics HMDScience.com Diffraction ©Andrew Douglas/Masterfile (br) ©Don Farrall/Photodisc/Getty Images Why It Matters 517 CONNECTING TO HISTORY satisfactory. By the early 1800s, the wave model began to replace the particle model because it Untitled-295 517 Isaac Newton is famous for his accomplishments 5/20/2011 7:54:17 AM in mechanics, especially the laws of gravitation could explain more phenomena about light. The and of motion. During his lifetime, however, he wave model explains not only reflection and was most famous for his work on light. Newton refraction but also diffraction and interference. thought of light as a beam of tiny particles. With After briefly explaining this history to this model, reflection was explained as particles students, ask them if they can think of other bouncing off a surface; refraction was explained scientific models that have changed over time. as caused by forces from the surface acting on Why do scientific models change? What makes light particles. As more became known about one model better than another? light, Newton’s particle model became less Interference and Diffraction 517 SECTION 1 SECTION 1 Objectives Plan and Prepare Describe how light waves Interference interfere with each other to produce bright and dark fringes. Preview Vocabulary Key Terms Identify the conditions required coherence path difference order number Visual Vocabulary Ask students to for interference to occur. visualize the iridescence of materials such Predict the location of Combining Light Waves as mother-of-pearl or the inside of an interference fringes using the You have probably noticed the bands of color that form on the surface of abalone seashell (show pictures or equation for double-slit a soap bubble, as shown in Figure 1.1. Unlike the colors that appear when examples if possible). Bands of color are interference. light passes through a refracting substance, these colors are the result of formed because each wavelength is light waves combining with each other. reinforced at a different position. This is known as interference. Explain that Interference takes place only between waves with the same wavelength. iridescence is caused by interference, and FIGURE 1.1 To understand how light waves combine with each other, let us review relate it to the other vocabulary from the Interference on a Soap how other kinds of waves combine. If two waves with identical wave- chapter. Bubble Light waves interfere lengths interact, they combine to form a resultant wave. This resultant to form bands of color on a soap wave has the same wavelength as the component waves, but according to bubble’s surface. the superposition principle, its displacement at any instant equals the sum of the displacements of the component waves. The resultant wave is Teach the consequence of the interference between the two waves. Figure 1.2 can be used to describe pairs of mechanical waves or electromagnetic waves with the same wavelength. A light source that has a single wavelength is called monochromatic, which means single Demonstration colored. In the case of constructive interference, the component waves combine to form a resultant wave with the same wavelength but with an INTERFERENCE IN SOUND WAVES amplitude that is