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Introduction to Light and Electormagnetic Waves Exercises Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. ____ 1. Electromagnetic waves are a. transverse waves. b. longitudinal waves. ____ 2. Electromagnetic waves a. need a medium to travel through. b. can travel through a vacuum. ____ 3. Which of these electromagnetic waves has the shortest wavelength? a. Infrared waves b. Light waves c. Radio waves d. X-rays e. Ultraviolet waves ____ 4. Compared to the wavelength of ultraviolet waves, the wavelength of infrared waves is a. the same. b. shorter. c. longer. ____ 5. Compared to the velocity of radio waves, the velocity of visible light waves is a. slower. b. faster. c. the same. ____ 6. The source of all electromagnetic waves is a. magnetic fields. b. heat. c. electric fields. d. vibrating charges. e. none of the above ____ 7. Which of the following are fundamentally different from the others? a. Gamma rays b. Radio waves c. Sound waves d. Light waves e. X-rays ____ 8. The main difference between a radio wave and a light wave is its a. speed. b. wavelength. c. both A and B d. none of the above. ____ 9. The main difference between a radio wave and a sound wave is its a. basic nature. b. c. d. e. amplitude. energy. frequency. wavelength. ____ 10. If the sun were to disappear right now, we wouldn't know about it for 8 minutes because it takes 8 minutes a. to operate receiving equipment in the dark. b. for light to travel from the sun to Earth. c. for the sun to disappear. d. all of the above e. none of the above ____ 11. Which of the following is NOT an electromagnetic wave? a. Sound b. Radio c. Light d. Infrared e. X-ray ____ 12. Heat lamps give off mostly a. X-rays. b. infrared waves. c. ultraviolet waves. d. microwaves. e. radio waves. ____ 13. Compared to its speed in air, the speed of light in water is a. slower. b. the same. c. faster. ____ 14. Glass is transparent to visible light, but not to a. ultraviolet. b. infrared. c. both a and b. d. none of the above ____ 15. The shiny surfaces of metals have most to do with a. metals' relatively high density. b. a resonant frequency of electrons in the metal. c. the fact that light reflects from metals. d. the free electrons in metal atoms. ____ 16. Clouds a. neither block nor transmit UV light. b. block UV light. c. transmit UV light. ____ 17. Electromagnetic waves with higher frequencies have wavelengths that are a. shorter. b. longer. ____ 18. The shadow produced by an object held close to a piece of paper in sunlight will be a. sharp. b. fuzzy. ____ 19. Solar eclipses are seen less commonly than lunar eclipses because a. the sun is so much larger than the moon. b. the sun is farther from Earth than is the moon. c. solar eclipses don't happen as often as lunar eclipses. d. Earth's shadow on the moon is larger than the moon's shadow on Earth. e. none of the above ____ 20. Light waves are a. longitudinal waves. b. transverse waves. ____ 21. What is the ultimate source of electromagnetic waves? a. Vibrating atoms b. Vibrating molecules c. Radio sets d. Vibrating charged particles e. TV antennas ____ 22. The primary purpose of polarized sunglasses is_____. a. to block ultraviolet rays. b. to block infrared rays. c. to block glare from reflections. d. to look cool. ____ 23. Light does not pass through what kind of materials? a. transparent b. opaque c. neither a nor b ____ 24. How far is a light-second? a. 5000 km b. 300,000 km c. 9,000,000 km d. 18,000,000 km e. 95,000,000,000 km ____ 25. Light that reflects at glancing angles from nonmetallic surfaces, such as glass, water, or roads is a. polarized perpendicular to the surface. b. polarized parallel to the surface. c. randomly polarized. ____ 26. Light reflected from a lake surface is polarized a. randomly. b. horizontally. c. vertically. ____ 27. If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a a. frequency of 1000 Hz. b. speed of 1000 m/s. c. period of 1000 s. d. wavelength of 1000 m. ____ 28. What is the wavelength of an electromagnetic wave that has a frequency of 1 Hz? a. More than 1 m b. Less than 1 m c. 1 m ____ 29. What is the frequency of an electromagnetic wave having a wavelength of 300,000 km? a. More than 1 Hz b. Less than 1 Hz c. 1 Hz ____ 30. After randomly polarized light passes through a polarizer, it is a. totally blocked. b. totally polarized. c. randomly polarized. d. partially polarized. ____ 31. If two polarizing filters are held with their polarization axes at right angles to each other, the amount of light transmitted compared to when their axes are parallel is a. zero. b. half as much. c. the same. d. twice as much. Essay 32. Which waves are part of the electromagnetic spectrum? What are their approximate frequencies? Give examples of where you can find each kind of wave. 33. Explain how light is transmitted through glass. Why is ultraviolet radiation not transmitted through glass? 34. Write a short paragraph on polarization. Explain what it is and how we use polarizers. Explain why sunglasses polarize light vertically. Introduction to Light and Electormagnetic Waves Exercises Answer Section MULTIPLE CHOICE 1. ANS: STO: 2. ANS: STO: 3. ANS: STO: 4. ANS: STO: 5. ANS: STO: 6. ANS: STO: 7. ANS: STO: 8. ANS: STO: 9. ANS: STO: 10. ANS: OBJ: 11. ANS: STO: 12. ANS: STO: 13. ANS: STO: 14. ANS: STO: 15. ANS: STO: 16. ANS: STO: 17. ANS: STO: 18. ANS: 19. ANS: 20. ANS: STO: 21. ANS: STO: 22. ANS: STO: 23. ANS: A Ph.4.b B Ph.4.e D Ph.4.e C Ph.4.e C Ph.4.e D Ph.4.e, Ph.4.f C Ph.4.e B Ph.4.e A Ph.4.e B 27.2 A Ph.4.e B Ph.4.e A Ph.4.e, Ph.4.f C Ph.4.e, Ph.4.f D Ph.4.b, Ph.4.f C Ph.4.b, Ph.4.f A Ph.4.e A D B Ph.4.b D Ph.4.e C Ph.4.b B DIF: 1 REF: p. 414 OBJ: 27.7 DIF: 2 REF: p. 407 OBJ: 27.2 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 409 OBJ: 27.4 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 STO: Ph.4.e DIF: 2 REF: p. 406, p. 407 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 410 OBJ: 27.4 DIF: 2 REF: p. 410 OBJ: 27.4 DIF: 2 REF: p. 411 OBJ: 27.5 DIF: 2 REF: p. 411 OBJ: 27.5 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 1 DIF: 3 DIF: 1 REF: p. 412 REF: p. 413 REF: p. 414 OBJ: 27.6 OBJ: 27.6 OBJ: 27.7 DIF: 2 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 414 OBJ: 27.7 DIF: 1 REF: p. 411 OBJ: 27.5 STO: 24. ANS: STO: 25. ANS: STO: 26. ANS: STO: 27. ANS: STO: 28. ANS: STO: 29. ANS: STO: 30. ANS: STO: 31. ANS: OBJ: Ph.4.b, Ph.4.f B Ph.4.e B Ph.4.b B Ph.4.b A Ph.4.e, Ph.4.f A Ph.4.e C Ph.4.e B Ph.4.b A 27.7 DIF: 3 REF: p. 407 OBJ: 27.1 DIF: 2 REF: p. 415 OBJ: 27.7 DIF: 2 REF: p. 415 OBJ: 27.7 DIF: 2 REF: p. 409 OBJ: 27.4 DIF: 3 REF: p. 408 OBJ: 27.3 DIF: 3 REF: p. 408 OBJ: 27.3 DIF: 2 REF: p. 414 OBJ: 27.7 DIF: 2 STO: Ph.4.b REF: p. 414, p. 415 ESSAY 32. ANS: Radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays are all part of the electromagnetic spectrum. Their approximate frequencies are 103 to 106 Hz, 107 to 1010 Hz, 1011 to 1014 Hz, 1014 Hz, 1015 to 1016 Hz, 1017 Hz, and 1018 Hz respectively. Radio waves are emitted at radio broadcast towers, and microwaves in microwave ovens. Microwaves are also used to transmit TV and information signals across Earth and between Earth and satellites. Infrared, visible, and ultraviolet waves are found in sunlight. X-rays are found in medical laboratories and also are emitted from most stars and galaxies. Gamma rays are emitted by nuclear reactions in laboratories and in reactors. DIF: 3 REF: p. 408 OBJ: 27.3 STO: Ph.4.e 33. ANS: Visible light is transmitted through glass by molecules that do not easily absorb light photons. A light photon is absorbed for a very short time by a glass molecule, but then it is reemitted in the same direction it was originally traveling and with the same frequency it originally had. This process continues until the photon finally emerges from the other side of the glass. Ultraviolet radiation is in the range of frequencies that resonate with atoms. Glass atoms hold onto UV energy for millions of vibrations, during which time the energy is passed to neighboring atoms by many collisions. The transmitted energy takes the form of heat instead of light. So glass is not transparent to ultraviolet radiation. DIF: 3 REF: p. 409, p. 410 OBJ: 27.4 STO: Ph.4.e, Ph.4.f 34. ANS: Electric field vectors of an electromagnetic wave vibrate in a plane. When many electromagnetic waves are present at once, electric field vectors are vibrating in many different planes. A polarizer is a material that absorbs electromagnetic radiation and passes only radiation that is vibrating in a certain plane. We decrease the amount of light entering our eyes by using sunglasses that allow only vertically polarized light to pass. A large fraction of reflected light is horizontally polarized, so sunglasses help reduce glare from reflected light. DIF: 3 REF: p. 414, p. 415 OBJ: 27.7 STO: Ph.4.b