Name Date Hour Chapter 15 Answer Key Ch.15-18 Guided Reading Sound and Light 1. Compare the speed of sound as it travels within a liquid, a solid, and a gas. Why does the speed of sound differ? Sound travels fastest through solids, at an intermediate rate in liquids, and slowest between gas molecules. This happens because solids are in general more elastic than liquids, which, in turn, are more elastic than gases. 2. If a small piece of space debris were to strike a space station, workers on the inside might hear the sound made by the collision, but workers outside the station would not. Explain. In the space station, the sound would be transmitted through the air; outside there is no air or other media to transmit the sound to the workers. 3. How are pitch and frequency of a sound related? While the pitch of a note is directly proportional to the frequency, pitch is also affected by an individual s brain and ear. The pitch a person hears is determined, in part, by the sounds that precede and follow the sound in question. 4. Your parents complain that the rap you are listening to is not music. Based upon the information in this section, what thoughts can you offer to support your choice of music? According to the text, music is a combination of sound and rhythm that an individual finds pleasant. If rap has both rhythm & sound and is pleasing to you, it can be considered music. That which is pleasing to you may not be to your parents, therefore it might not music to them even though it is to you. 5. As you tune your clarinet, you hear an oscillating sound your instructor calls beats. What causes them and how can you use them to tune your instrument? Beats occur when two notes being played simultaneously are very close to the same frequency. Alternating constructive and destructive interference between superposed waves cause the beats. If you listen to the frequency to which you are to tune your instrument and adjust your clarinet so that no beats are heard, the two frequencies are the same. 6. Why does an A played on a piano not sound exactly like an A produced by a guitar? The sound produced by most sources is a combination of many frequencies. While the fundamental note produced by each source is an A, each source produces its own combination of harmonics that also differ in rise and fall times from one instrument to the next. Each combination is characteristic of a specific instrument. 7. A steel string does not produce a loud sound by itself. Explain how an acoustic guitar produces a loud sound when a string is plucked. The string is attached to the body of an acoustic guitar. The vibrating string causes the body to vibrate at the same frequency that moves a greater volume of air than the string by itself. Also, the hollow body of the guitar produces louder sound through resonance with the many frequencies produced by the vibrating strings.
8. How does an electric guitar pickup produce an amplified sound? As the steel string vibrates, it passes through the magnetic field of the pickup, inducing an oscillating electric current whose frequency is that of the vibrating string. The current is amplified to produce a loud sound. 9. The decibel scale is used to measure the loudness of a sound. How is loudness (the decibel scale) of a sound related to the amplitude of the sound wave? For each increase of 20 db on the decibel scale, there is a corresponding ten-fold increase of amplitude in the pressure wave. 10. Most people know that sound is a wave. List at least three pieces of evidence to support the idea that sound is a wave. - Sound has a frequency we can hear and a wavelength we can verify by experiment. - The speed of sound can be calculated as the product of frequency and wavelength. - Sound shows evidence of diffraction & interference, characteristic of wave motion. - Resonance can be demonstrated for sound. 11. How is the wavelength of sound produced by a musical wind instrument related to the size of the instrument? If the instrument is closed on one end (has a closed boundary), the instrument will produce resonance for a wave that is approximately 4 x s as long as the instrument. 12. Explain the two diagrams below. (HINT: Look back to Chapter 14.) Constructive interference When two wave pulses on the same side add up to make a single, bigger pulse when they meet. Destructive interference Two equal wave pulses on opposite sides subtract when they meet. The upward movement of one pulse exactly cancels with the downward movement of the other. For a moment there is no pulse at all. 13. A patron at a concert claims that she cannot hear clearly certain notes being played unless she moves her head slightly to one side or the other. Explain how this could happen. Sounds coming from an instrument may be reflected from several surfaces in a concert hall. If the path length difference from the points of reflection to the patron is an odd number of half wavelengths, the reflections arrive out of phase at her location, destructive interference will occur, & the sound may be much quieter at that spot. 14. Parents are concerned for the hearing of their children who wear stereo headsets adjusted to high volume settings. Using Table 15.1, explain why their concerns are justified. The table summarizes pressure changes that accompany sounds of various intensities. A change in pressure of 2 10 9 atmospheres can be detected as a 20 db sound. In fact, a loud sound of 120 db represents an increase of pressure to only 2 10 4 atmospheres. That even loud sounds represent only small pressure changes suggests that the structure of the ear is a delicate mechanism. Continued exposure to loud sounds can damage it. 15. When an astronomer observes the sun, she notices that the light from one edge is slightly shifted toward the red end of the visible spectrum while the opposite edge is slightly shifted toward violet. What causes this shift? The sun is spinning on its axis. (One edge is moving toward the observer while it spins while the other moves away.) The Doppler shift causes the observer to see a higher frequency (more blue & violet) light coming from the edge moving toward the observer. Light from the other edge is shifted toward the red as it moves away.
16. As the temperature increases, the fundamental frequency produced by a flute changes slightly. Does it increase or decrease? It will increase slightly. Give an explanation for your answer. As the temperature increases, the speed of sound increases. Since the instrument maintains a nearly constant length, the wavelength reinforced remains constant. The frequency must increase in proportion to the increased velocity. 17. What causes consonance and dissonance? Two frequencies of sound occurring simultaneously in the same medium cause beats. If the frequencies are nearly the same, the beats are obvious, and the sound produced is generally irritating, or dissonant. If the frequencies are quite different, the beats are not discernible, and the sound is, in general, pleasing or consonant. Chapter 16 1. How is an incandescent bulb different from a fluorescent bulb? An incandescent bulb generates light and also a great deal of heat. A fluorescent bulb generates light and only a small amount of heat. 2. In what units is light intensity measured? watts per square meter (W/m 2 ) 3. You wish to read a book in your bedroom. There is enough light for you to read if you use either a 100 W ceiling light or a 15 W desk lamp. Both use the same type of bulb. Explain why you can read with the less powerful desk lamp. You can read with the desk lamp because it is closer to the book than the ceiling light is. Even though the desk light has less power, the intensity of the light on the book is great because it is a small distance away. 4. List three ways light can be used for communication. Television, lasers, and fiber-optic cables use light for communication. 5. Why do we see lightning before we hear thunder? We see lightning before hearing thunder because light travels much faster than sound. 6. Compare reflection and refraction. Reflection is the bouncing of incident light off a surface. Refraction is the bending of light when it moves from one material into another material. 7. What is white light? White light is the combination of all colors of light. 8. How could a blacksmith tell the temperature of a fire long before thermometers were invented? A blacksmith uses color of the fire as a reference. When the fire appears red, it is a relatively low temperature; when it appears blue, it is a relatively high temperature. 9. Why is it difficult to distinguish among different colors in a dimly lit room? Cone cells in our eyes respond to color. They are not as sensitive as rod cells, so the cones do not work well in a dimly lit room. Therefore, it is difficult to distinguish among different colors. 10. How can we see many different colors if our eyes only contain three types of cones? Our eyes can see many colors because all colors of light are combinations of red, green, and blue light. Depending on its color, light can stimulate more than one type of cone. Our brains receive these combined signals and perceive different colors. 11. Add the colors of light: a. red + blue = Magenta b. blue + green = Cyan c. red + green = Yellow d. red + blue + green = White
12. Why is mixing pigments called color subtraction? Mixing pigments is called color subtraction because pigments absorb some colors and reflect others. When pigments are mixed, they subtract more colors of light. 13. What color results when cyan, magenta, and yellow pigments are mixed? White 14. Answer true or false for each: a. A green object reflects green light. True c. A yellow object reflects green light. True b. A blue object absorbs red light. True d. A white object absorbs red light. False 15. Why is it a good idea to wear a white shirt rather than a black shirt on a hot sunny day? A white shirt reflects most of the light and keeps the person cool on a hot sunny day while a black shirt absorbs all of the light and makes the person hot. 16. Why will a plant grow more quickly if it is grown in white light rather than green light? Chlorophyll in a plant reflects green light, so the plant will not absorb enough energy if placed in green light. But chlorophyll absorbs light of other colors, so it grows faster if placed in white light. 17. Explain how a television makes pictures of many colors using only three types of pixels. A television s three types of pixels give off red, green, and blue light. By turning on the different color pixels in different amounts, the TV mixes the three colors and produces pictures of many colors. 18. Use the photon theory of light to describe 2 ways to create high intensity with both high energy and low energy photons? One way to make high intensity light is to have high-energy photons; the other is to have a large number of low-energy photons. 19. Explain how glow-in-the-dark materials work. When the glow-in-the-dark plastic is exposed to light, phosphorus atoms absorb the energy from the photons they receive. Then those atoms slowly release the stored energy and the plastic glows. Chapter 17 1. State the law of reflection. Angle of reflection equals to the angle of incidence. Does this law hold true for specular reflection? YES, this law holds true for specular reflection Does it hold true for diffuse reflection? NO, the law does not hold true for diffused reflection. 2. Refer to the diagram below. State the correct term for each item listed: a. Line A-B Incident ray b. Line D-B Normal line c. Line B-C Reflected ray d. Angle F Angle of incidence e. Angle G Angle of reflection
3. Use the diagram to answer the following questions: a. If A is a real object in front of a mirror, is B a real image or a virtual image? Virtual image b. Line 1-2 is the incident ray from the object to the mirror. Identify the corresponding reflected ray. Line 2-3 c. Line 1-2 is the incident ray from the object to the mirror. Identify the ray that our eye creates to allow us to see the virtual image. Line 3-4 d. Object A is 8 cm in front of the mirror. How far away is the image from the object? 8 cm 4. Refer to Table 17.1 in the text. Which material has a greater ability to bend light, ice or glass? Glass Which material listed has the greatest ability to bend light? Diamond How do you know? The greater the index of refraction, the greater the ability to bend light 5. Consider the diagram shown. Ray A-B represents the incident ray. Identify the refracted ray in each case: a. n 1 is greater than n 2 C b. n 1 is equal to n 2 D c. n 1 is less than n 2 E 6. Explain how fiber optic cables utilize the properties of reflection and refraction. Fiber optic cables are made of thin glass fibers. When light enters a glass fiber with an angle greater than the critical angle, it repeatedly reflects off the wall due to total internal reflection. The beam of light then travels from one end of the fiber to the other. 7. When white light passes through a prism, which color refracts more, yellow or green? Green light refracts more because it has a greater index of refraction. 8. The diagram below shows an object to the left of a converging (+) lens and the real image produced to the right of the lens. Use the diagram to identify the following rays: a. The ray of light that travels from the object to the lens along a line parallel to the optical axis. ABG b. The ray of light that travels from the object to the center of the lens. ACF c. The ray of light that travels from the object through the focal point to the lens. ADE 9. What determines the amount of refraction (bending) that takes place when a light ray passes from one substance to another? The amount that light bends as it passes from one substance into another depends on the difference between the index of refraction of the substances. A larger difference causes greater refraction.
Chapter 18 1. Describe an electromagnetic wave. An electromagnetic wave consists of oscillating electric and magnetic waves that travel together perpendicular to each other at the speed of light, 90 out of phase, and at the same frequency and wavelength. 2. Add to the diagram below to show the different types of electromagnetic energy from highest energy to lowest energy. Radio/TV waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma Rays 3. Which color of visible light has the highest frequency? The color with the highest frequency is violet, Which has the lowest frequency? The color with the lowest frequency is red. Compare the wavelengths of these two colors. The wavelength of violet is smaller than that of red. 4. True or False: All electromagnetic waves travel at the same speed in a vacuum. True Bonus Questions! 1. In your own words, define the following terms. (Use your memory the answers are not in the book!) Transparent: When light passes through an object and exists relatively unchanged. Translucent: When light passes through an object and exists scattered. Opaque: When light does not pass through and object. 2. Explain why radio waves can travel through space, but sound waves cannot. A radio wave is an electromagnetic wave; can travel in a vacuum (empty space). A sound wave is a longitudinal wave; must have a medium (molecules) to transmit. 3. Apply what you have learned to answer the following two questions. Why do you think the sky appears blue during the day? The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. However, the gas molecules absorb much of the shorter wavelength light. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. Why does the image of the Sun sometimes appear reddish at sunrise and sunset? As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes. 4. Why does the ground and atmosphere get warm during the day? Electromagnetic energy from the sun (mostly in the form of visible light and infrared radiation) is absorbed into the ground and re-radiated into the atmosphere. 5. How do you hear a distant sound? How is it different from how you hear a sound nearby? Sound transmits through the molecules of the atmosphere. As it travels, the molecules absorb some of the energy; therefore sounds that are distant are much softer than sounds generated nearby.