Hobson Physics: Concepts & Connections 4e

CHAPTER 9 review questions Electromagnetic Waves 1. Make a list of phenomena that are caused by electric charge. 2. What is an electromagnetic wave, and how fast does it go? 3. Are electromagnetic fields physically real? Defend your answer. 4. Describe the ether theory of light. 5. In what way do electromagnetic waves violate the philosophical underpinnings of Newtonian physics? The Complete Spectrum 6. List the six main regions of the spectrum, from longest to shortest wavelength. 7. Describe a typical source of each: X rays, infrared, gamma rays, radio waves, and ultraviolet. 8. Describe physically how humans see. 9. List several practical applications of radio waves. 10. Which parts of the spectrum are ionizing radiations? 11. Which three regions of the spectrum dominate solar radiation? Which single region dominates? Global Ozone Depletion 12. Where does ozone occur naturally on Earth, and what is its human significance? 13. What are CFCs? How have they been useful to humans? 14. Outline the process by which CFCs destroy ozone. 15. List three atmospheric trace gases. 16. What is the Ozone Treaty? 17. List some expected effects of ozone depletion. Global Warming 18. What are the two major greenhouse gases, and what property makes them greenhouse gases? 19. What would happen if we removed all the from the atmosphere? All the ozone? 20. Explain the greenhouse effect. 21. Which would increase global warming, forestation or deforestation? Why? Would this also increase ozone depletion? 22. What is a feedback effect? Describe one feedback effect related to global warming. 23. List three recommendations that have been made to combat global warming. conceptual exercises Electromagnetic Waves 1. What evidence is there that the medium that carries light waves is not air? 2. Imagine a region of space that had no atoms and no subatomic particles. Would it contain matter? Might it contain energy? 3. Which travels faster, light or radio waves? Which has a longer wavelength? Which has a higher frequency? 4. It takes light 20 minutes to travel from Mars to Earth (depending on where Mars and Earth are in their orbits). How might this affect a conversation between an astronaut on Mars and people on Earth? Suppose an ultra-powerful telescope were used for visual communication. Would this speed things up? 5. Are radio waves filling your room right now? Describe a simple experiment that could demonstrate your answer. 6. If your ears actually detected radio waves instead of sound waves, what would your ears be “hearing” right now? 7. List three characteristics that all electromagnetic waves have in common. 8. Light from the sun takes roughly 8 minutes to reach Earth, while light from Alpha Centauri, the nearest star beyond the sun, takes about 4 years. How many times farther is it to Alpha Centauri than it is to the sun? 9. Using the data in the preceding problem, about how far is it to Alpha Centauri in kilometers? The Complete Spectrum 10. Is there any physical difference between light and a radio wave? Explain. 11. You can get a sunburn even on a cloudy day. Why? 12. You do not get a sunburn, even on a sunny day, if you are behind glass. Why? 13. What kinds of animals might evolve on a planet orbiting a star whose radiation is mostly in the infrared? 14. Suppose you viewed Earth’s dark side from space. Could you “photograph” Earth using ultraviolet-sensitive film? Light-sensitive film? Infrared-sensitive film? If so, what would you expect to see in the photo? 15. What energy transformation occurs (from what type to what type?) when solar radiation warms your skin? In a flashlight? When microwaves warm your food? 16. Your radio is tuned to 92 on the FM dial. What frequency of electromagnetic wave is your radio receiving? How fast is this wave traveling? About how long is one wavelength? Does an electromagnetic wave actually reach your ear? What does reach your ear? Global Ozone Depletion 17. Which of these worsens the ozone problem: coal-fired power plants, gasoline engines, CFC coolants, nuclear power plants, hydroelectric power plants, solar heating of homes, deforestation? 18. Why is it important that spray-can aerosols be propelled by inert gases? Why does the inertness of CFCs lead to problems with stratospheric ozone? 19. According to Table 9.2, which will be the first ozone-destroying chemical to decrease to harmless levels, and how long will it take? Which will be the last, and how long will it take? 20. What was the chlorine concentration in 1950? Under the Ozone Treaty, what is the highest predicted level? When is the level predicted to return to the 1975 level? What would the level be at that time if there were no Ozone Treaty? 21. Which of the ozone-destroying chemicals has the longest atmospheric lifetime? Which one forms the largest share of the problem? 22. Ozone, typically “lives” for only 100 to 200 seconds in the stratosphere before reacting with an O atom to form two molecules of Since it is so short-lived, how can it offer any protection from ultraviolet radiation? 23. The total quantity of energy that reaches Earth in the infrared region is greater than that in the ultraviolet region. Why then are we more concerned about the direct health effects of UV than of IR? 24. One cubic centimeter of normal air at Earth’s surface contains about molecules. Working from Table 9.1, find the number of molecules in of air. Do the same for ozone, which has an atmospheric concentration of 0.3 ppm. 25. Following up on the preceding question, find the number of molecules in of air. Global Warming 26. Which of these automobile fuels would not contribute to global warming: natural gas, synthetic gasoline made from coal, electricity from a solar power plant, electricity from a coal power plant, electricity from a nuclear power plant, ethanol (grain alcohol) made from corn? 27. What are some alternatives to burning fossil fuels? Consider electric power generation, transportation, home heating. 28. Will the Ozone Treaty help in solving global warming? How? 29. Which of these contributes to global warming: coal-fired power plants, gasoline engines, CFC coolants, nuclear power plants, hydroelectric power plants, solar heating of homes, deforestation? 30. It has been suggested that global warming could affect the concentration in the oceans. What evidence is there in your everyday environment to show that can be dissolved in water? As the temperature is raised, would you expect the amount of dissolved to increase, decrease, or remain the same? If this effect happens in ocean water, will it represent a positive or negative feedback on global warming? 31. According to Figure 9.20, how far back before the present century must one go to find a time when the concentration was above its preindustrial value of 280 ppm? How large was the concentration at that time? How did the temperature at that time compare with present temperatures? 32. Assuming that differences in emissions listed in Figure 9.25 are due only to differences in fossil-fuel use, how many joules of fossil energy are consumed by a typical American for each joule consumed by a typical Japanese? How many joules are consumed by a typical Japanese for each joule consumed by a typical Indian? 33. According to Figure 9.26, by what total percentage would U.S. emissions be reduced if cogeneration of heat and electricity were vigorously pursued? What if all three listed transportation options were vigorously pursued? problems Electromagnetic Waves 1. How long does it take a radio signal to travel from New York to San Francisco, about 5000 km? 2. A radar transmitter pointed at the moon receives a reflection 3 seconds after the signal is sent. How far is it to the moon? 3. Find the radius of Earth’s orbit from the fact that light gets here from the sun in 8.3 minutes. 4. What is the time delay for a television signal that is sent via satellite? Communications satellites orbit above the equator in circles of radius 36,000 km (six times larger than Earth’s radius!). To simplify the problem, assume that the signal goes straight up and straight down. 5. Use the formula (Chapter 8) to find the wavelength of 60 Hz power-line radiation. 6. Find the wavelength of microwaves (see Figure 9.5). 7. The wavelength of light from sodium vapor lamps is 589 “nanometers” (a nanometer is What is its frequency? 8. Find the wavelength of blue-green light having a frequency of How does this wavelength compare with the size of an atom, which is about Ozone Depletion and Global Warming 9. To better understand the meaning of 1 ppm, consider krypton, which has an atmospheric concentration of 1 ppm. One cubic centimeter of normal air at Earth’s surface contains about molecules. Find the number of krypton atoms in a cubic centimeter of normal air. 10. Making estimates. The mass of 1 liter of gasoline is about 0.7 kg, and the mass of 1 gallon is about 2.5 kg. Assuming that gasoline is pure carbon (actually only about 85% of its mass is carbon), estimate the mass of carbon a typical automobile puts into the atmosphere each year. Compare with Figure 9.25.