Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science Chapter 8 WAVES—SOUND AND LIGHT

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley This lecture will help you understand: Vibrations and Waves Wave Motion Transverse and Longitudinal Waves The Nature of Sound Resonance The Nature of Light Reflection Transparent and Opaque Materials Color Refraction Diffraction Interference The Doppler Effect The Wave–Particle Duality

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Vibrations and Waves Vibration: a wiggle in time Wave: a wiggle in space and time—a disturbance that travels from one place to another transporting energy.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Vibrations and Waves Description: Vibration in terms of frequency—how frequently vibratory motion occurs Wave in terms of its frequency, speed, amplitude, and wavelength

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Vibrations and Waves Frequency: number of to-and-fro vibrations in a given time Unit: 1 vibration per second = 1 Hertz Period: defined as the time it takes for a complete vibration Unit: any unit of time, often the second

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Vibrations and Waves Relationship between frequency and period: Frequency = 1/period Unit: Hertz (Hz) Period = 1/frequency Unit: second (s) The source of all waves is a vibration. Higher frequency means increased rate of energy transfer. Pulses occur more frequently and produce waves that are more closely spaced—shorter wavelengths.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If the frequency of a particular wave is 20 Hz, its period is A. 1 / 20 second. B.20 seconds. C.more than 20 seconds. D.none of the above. Vibrations and Waves CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If the frequency of a particular wave is 20 Hz, its period is A. 1 / 20 second. B.20 seconds. C.more than 20 seconds. D.none of the above. Explanation: Note when  = 20 Hz, T = 1/  = 1/(20 Hz) = 1 / 20 second. Vibrations and Waves CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Wave Motion Wave motion: the propagation of a disturbance through a medium medium transporting the wave returns to initial condition after disturbance has passed requires an energy source, and a medium (except for light) through which the energy is transferred

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Wave Motion Wave characteristics: crest—highest point trough—lowest point wavelength amplitude frequency period

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The distance between adjacent peaks in the direction of travel for a transverse wave is its A.frequency. B.period. C.wavelength. D.amplitude. Wave Motion CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The distance between adjacent peaks in the direction of travel for a transverse wave is its A.frequency. B.period. C.wavelength. D.amplitude. Explanation: The wavelength of a transverse wave is also the distance between adjacent troughs, or between any adjacent identical parts of the waveform. Wave Motion CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Wave Motion Wave speed: describes how fast the disturbance moves through the medium is related to frequency and wavelength of the wave Equation for wave speed: Wave speed = frequency  wavelength v = 

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Transverse and Longitudinal Waves Two different types of waves classified in the direction in which the medium vibrates compared to the direction of energy travel: Transverse wave: Vibration is in right angles (sideways) to wave travel. Longitudinal wave: Vibration is in the direction of travel. Wave travel consists of compression and rarefaction components.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The vibrations along a transverse wave move in a direction A.along the wave. B.perpendicular to the wave. C.both of the above. D.neither of the above. Transverse and Longitudinal Waves CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The vibrations along a transverse wave move in a direction A.along the wave. B.perpendicular to the wave. C.both of the above. D.neither of the above. Comment: The vibrations in a longitudinal wave, in contrast, are along (or parallel to) the direction of wave travel. Transverse and Longitudinal Waves CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Nature of Sound Sound travels in longitudinal waves consisting of vibrating compressions and rarefactions through the air. Speed of Sound Sound travels at 340 m/s in air at 20°C.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Consider a person attending a concert that is being broadcast over the radio. The person sits about 45 m from the stage and listens to the radio broadcast with a transistor radio over one ear and a nonbroadcast sound signal with the other ear. Further suppose that the radio signal must travel all the way around the world before reaching the ear. The Nature of Sound A situation to ponder…

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which signal will be heard first? A.Radio signal. B.Nonbroadcast sound signal. C.Both at the same time. D.None of the above. A situation to ponder… CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which signal will be heard first? A.Radio signal. B.Nonbroadcast sound signal. C.Both at the same time. D.None of the above. Explanation: A radio signal travels at the speed of light—3  10 8 m/s. Time to travel 45 m at 340 m/s ≈ 0.13 s. Time to travel 4  10 7 m (Earth’s circumference) at 3  10 8 m/s ≈ 0.13 s. So if you sit farther back at the concert, the radio signal would reach you first! A situation to ponder… CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Nature of Sound For each increase of 1 ° C above 0 ° C, speed of sound increases by 0.6 m/s. Order of increasing speeds of sound: in air (≈ 340 m/s) in warm air (>340 m/s) in water (≈ four times speed in air) in steel (≈ 15 times speed in air)

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Resonance occurs whenever successive impulses are applied to a vibrating object in rhythm with its natural frequency.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Nature of Light Light: electromagnetic waves created by vibrating electric charges having frequencies that fall within the range of sight the frequency of vibrating electrons equals the frequency of the light travels nearly a million times faster than sound in air light and all electromagnetic waves are transverse waves

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Nature of Light The Electromagnetic Spectrum

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The electromagnetic spectrum is a span of electromagnetic waves, ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A.radio waves. B.microwaves. C.visible light. D.gamma rays. The Nature of Light CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The electromagnetic spectrum is a span of electromagnetic waves, ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of A.radio waves. B.microwaves. C.visible light. D.gamma rays. Explanation: This can be inferred by a careful study of the spectrum and its regions in Figure The Nature of Light CHECK YOUR ANSWER

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The Nature of Light Order of increasing frequency of visible light: red violet—nearly twice the frequency of red ultraviolet—cause sunburns X-rays gamma rays

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Nature of Light Electromagnetic waves are composed of perpendicular electric and magnetic fields that vibrate perpendicular to the direction of wave travel. The electric and magnetic fields regenerate each other by electromagnetic induction.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley A photographer wishes to photograph a lightning bolt by setting his camera so that it is triggered by the sound of thunder. The Nature of Light A situation to ponder…

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Is this a good idea or a poor idea? A.Good idea for nearby lightning strikes. B.Good idea for all strikes. C.Poor idea for nearby lightning strikes. D.Poor idea for all strikes. A situation to ponder… CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Is this a good idea or a poor idea? A.Good idea for nearby lightning strikes. B.Good idea for all strikes. C.Poor idea for nearby lightning strikes. D.Poor idea for all strikes. Explanation: Light travels about a million times faster than sound. By the time the sound of thunder arrives, the lightning bolt is long gone. A situation to ponder… CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Reflection Reflection: the returning of a wave to the medium through which it came when encountering a reflective surface Law of reflection: angle of incidence = angle of reflection

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Reflection Diffuse Reflection When light is incident on a rough surface, it is reflected in many directions.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Compared with a dry road, seeing is difficult when driving at night on a wet road. Why? A.Wet surface is smooth with less diffuse reflection, part of which would otherwise reach the driver’s eyes. B.Wet road usually means a wet windshield. C.Wet road usually means more vapor in the air. D.There is no reason—that’s just the way it is. Reflection CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Compared with a dry road, seeing is difficult when driving at night on a wet road. Why? A.Wet surface is smooth with less diffuse reflection, part of which would otherwise reach the driver’s eyes. B.Wet road usually means a wet windshield. C.Wet road usually means more vapor in the air. D.There is no reason—that’s just the way it is. Reflection CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Transparent and Opaque Materials Transparent materials: glass and water—light passes through in straight lines, with atoms undergoing a series of absorptions and reemissions

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Transparent and Opaque Materials Opaque materials: colored glass is opaque to much of incident white light

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Color Color we see depends on frequency of light ranging from lowest (red) to highest (violet). In between are colors of the rainbow. Hues in seven colors: red, orange, yellow, green, blue, indigo, and violet. Grouped together, they add to appear white.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Color Selective Reflection Most objects don’t emit light, but reflect light. A material may absorb some of the light and reflect the rest. Selective Transmission The color of a transparent object depends on the color of the light it transmits.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Color Mixed Color Lights (Integrated) Three types of cone receptors in our eyes perceive color—each is stimulated by only certain frequencies of light: Light of lower frequencies stimulates the cones sensitive to low frequencies (red) Light of middle frequencies stimulates the cones sensitive to mid-frequencies (green) Light of high frequencies stimulates the cones sensitive to high frequencies (blue) Stimulation of all three cones equally, we see white light

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Color Additive primary colors (red, blue, green): red + blue = magenta red + green = yellow blue + green = cyan

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Color Opposites of primary colors: opposite of green is magenta opposite of red is cyan opposite of blue is yellow The addition of any color to its opposite color results in white.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley To which is the human eye blind? A.Infrared radiation. B.Ultraviolet radiation. C.Both A and B. D.Neither A nor B. Color CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley To which is the human eye blind? A.Infrared radiation. B.Ultraviolet radiation. C.Both A and B. D.Neither A nor B. Color CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Refraction Refraction: the bending of a wave due to a change in the medium and/or speed of the wave

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Refraction Examples of refraction: When light slows down in going from one medium to another, as when going from air to water, it bends toward the normal. When light speeds up in traveling from one medium to another, as when going from water to air, it bends away from the normal.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Refraction Sound waves refract when parts of the wave fronts travel at different speeds. Refraction occurs when sound waves are affected by uneven winds, or when air near the ground is warmer than air above.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Refraction Lenses are classified into two kinds: Converging lens incoming parallel light rays refract and converge to a focal point Diverging lens incoming parallel light rays refract in such a way that extended rays diverge to a focal point in front of the lens

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Diffraction Diffraction: Any bending of light by means other than reflection and refraction Smaller openings produce greater diffraction (greater bending of the waves at edges) Amount of diffraction depends on the wavelength of the wave compared to the size of the obstruction that casts the shadow

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Interference is the combined effect of two or more overlapping waves.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Interference Two types of interference: Constructive interference crest of one wave overlaps crest of another wave  individual effects add, resulting in a wave of increased amplitude Destructive interference crest of one wave overlaps the trough of another  individual effects are reduced

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Interference is a property of A.sound. B.light. C.both of these. D.neither of these. Interference CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Interference is a property of A.sound. B.light. C.both of these. D.neither of these. Explanation: See Figure 8.47 to see illustrations of both light and sound interference. Interestingly, the presence of interference tells a physicist whether something is wavelike or not. All types of waves can interfere. Interference CHECK YOUR ANSWER

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The Doppler Effect The Doppler Effect: a change in frequency as measured by an observer due to the motion of the source or listener Named after Austrian physicist and mathematician, Christian Johann Doppler

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Doppler Effect Example of Doppler Effect: The frequency of waves received by an observer increases as a sound source moves toward the observer. The wave frequency decreases as the source moves away.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a fire engine approaches you, the A.speed of its sound increases. B.frequency of sound increases. C.wavelength of its sound increases. D.all increase. The Doppler Effect CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a fire engine approaches you, the A.speed of its sound increases. B.frequency of sound increases. C.wavelength of its sound increases. D.all increase. Comment: Be sure you distinguish between sound, speed, and sound frequency. The Doppler Effect CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Doppler effect occurs for A.sound. B.light. C.both A and B. D.neither A nor B. The Doppler Effect CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Doppler effect occurs for A.sound. B.light. C.both A and B. D.neither A nor B. Explanation: As the text states, the Doppler effect occurs for sound (Figure 8.50) and for light (see the Integrated Science— Astronomy feature). Astronomers measure the spin rates of stars by the Doppler effect. The Doppler Effect CHECK YOUR ANSWER

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The Wave–Particle Duality In ancient times, Plato, other Greek philosophers, and Isaac Newton thought that light was composed of tiny particles. 100 years after Newton, Thomas Young demonstrated the wave nature of light with interference experiments. 25 years later, the wave view was confirmed by Heinrich Hertz. Later in 1905, Albert Einstein challenged the wave theory and stated that light was confined in tiny particles of energy called photons. His particle model of light was verified by the photoelectric effect.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Wave–Particle Duality Today, light is acknowledged to have both a wave nature and a particle nature— wave–particle duality: light reveals itself as a wave or particle depending on how it is being observed light behaves as a wave when traveling from a source to a place where it is detected and behaves as a stream of photons when it interacts with a detector

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Wave–Particle Duality The Photoelectric Effect When light shines on certain metal surfaces, electrons are ejected from those surfaces. Ultraviolet and violet light impart sufficient energy to knock electrons from those metal surfaces while lower-frequency light does not, even when very bright.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Why is unexposed black and white photographic film not “exposed” when in red light, but is when in white light? A.The red light in a dark room is usually too dim. B.Red light has insufficient energy per photon to “expose” the film. C.Red light is low-temperature light. D.None of the above. The Wave–Particle Duality CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Why is unexposed black and white photographic film not “exposed” when in red light, but is when in white light? A.The red light in a dark room is usually too dim. B.Red light has insufficient energy per photon to “expose” the film. C.Red light is low-temperature light. D.None of the above. The Wave–Particle Duality CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Wave–Particle Duality Findings: 1.ejection of electrons depended only on the frequency of light 2.the higher the frequency of the light, the greater the kinetic energy of ejected electrons Explanation: Electrons in the metal are bombarded by “particles of light”—photons. The energy of each photon is proportional to its frequency: E  .

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Light travels as a wave and is absorbed as a A.wave. B.particle. C.both of the above. D.none of the above. The Wave–Particle Duality CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Light travels as a wave and is absorbed as a A.wave. B.particle. C.both of the above. D.none of the above. Explanation: Light is wavelike as it travels but particle-like when it encounters a surface. The Wave–Particle Duality CHECK YOUR ANSWER