ch29 - CHAPTER 29 PARTICLES AND WAVES CONCEPTUAL QUESTIONS...

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CHAPTER 29 PARTICLES AND WAVES CONCEPTUAL QUESTIONS ____________________________________________________________________________________________ 1. REASONING AND SOLUTION A monochromatic light source emits photons of a single frequency. According to Equation 29.2, the energy, E , of a single photon is related to its frequency f by the relation , where h is Planck's constant. Eh f = The photons emitted by a source of light do not all have the same energy. Since the photons do not all have the same energy, then, from Equation 29.2, we can conclude that the photons do not all have the same frequency. Therefore, the source is not monochromatic. ____________________________________________________________________________________________ 2. REASONING AND SOLUTION According to the data given in Example 1, Chapter 24, the frequency of visible light ranges from 4 0 10 . × 14 Hz (red light) to (violet light). According to Equation 29.2, the energy, E , of a photon is related to its frequency, f , by the relation , where h is Planck's constant. According to Equation 29.2, the energy of a photon is directly proportional to its frequency. 7 9 10 . × 14 Hz f = a. The red-colored light bulb emits photons with the lowest frequency compared to light bulbs of other colors (orange, yellow, green, or blue); therefore, the red-colored light bulb emits photons with the lowest energy. b. The color blue appears next to violet in the continuous visible spectrum; therefore, the frequency of blue light is slightly smaller than that of violet, but greater than the frequency of other colors of the visible spectrum. Thus, the blue-colored light bulb emits photons with the highest frequency compared to the other light bulbs; therefore, the blue-colored light bulb emits photons with the greatest energy. ____________________________________________________________________________________________ 3. REASONING AND SOLUTION A photon emitted by a higher-wattage red light bulb does not have more energy than a photon emitted by a lower-wattage red bulb. The wattage of a bulb describes the power output of a bulb. Since average power is defined as energy per unit time, the power output of a light bulb tells us the rate at which the light bulb produces energy. According to Equation 29.2, the energy, E , of a photon is related to its frequency, f , by the relation , where h is Planck's constant. Thus, the energy of a photon depends only on the frequency of the associated light wave. The frequency of red light is the same, regardless of the rate of energy production; therefore, all photons of red light have the same energy, regardless of the nature of their source. f = Remark : Since the higher-wattage bulb provides more energy per unit time than the lower- wattage bulb, we can conclude that the higher-wattage bulb produces more photons per unit time. All of the "red photons," however, have the same energy. ____________________________________________________________________________________________
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Chapter 29 Conceptual Questions 1477 4. REASONING AND SOLUTION When a sufficient number of visible light photons strike a piece of photographic film, the film becomes exposed. An X-ray photon is more energetic than a visible light photon. Yet, most photographic films are not exposed by the X-ray machines used at airport security checkpoints. Since a single X-ray photon is more energetic than a single photon of visible light, we can conclude that the number of X-ray
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ch29 - CHAPTER 29 PARTICLES AND WAVES CONCEPTUAL QUESTIONS...

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