950_Physics ProblemsTechnical Physics

950_Physics ProblemsTechnical Physics - 34 Electromagnetic...

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34 CHAPTER OUTLINE 34.1 Maxwell’s Equations and Hertz’s Discoveries 34.2 Plane Electromagnetic Waves 34.3 Energy Carried by Electromagnetic Waves 34.4 Momentum and Radiation Pressure 34.5 Production of Electromagnetic Waves by an Antenna 34.6 The Spectrum of Electromagnetic Waves Electromagnetic Waves ANSWERS TO QUESTIONS Q34.1 Radio waves move at the speed of light. They can travel around the curved surface of the Earth, bouncing between the ground and the ionosphere, which has an altitude that is small when compared to the radius of the Earth. The distance across the lower forty-eight states is approximately 5 000 km, requiring a transit time of 51 0 10 6 2 × × m 31 0 m s s 8 ~ . To go halfway around the Earth takes only 0.07 s. In other words, a speech can be heard on the other side of the world before it is heard at the back of a large room. Q34.2 The Sun’s angular speed in our sky is our rate of rotation, 360 24 15 ° h h. In 8.3 minutes it moves west by θω ==° F H G I K J t 15 1 83 21 h h 60 min min bg af . . . This is about four
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