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Unformatted text preview: gonzales (pag757) Homework 12 Hoffmann (56745) 1 This printout should have 15 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Consider the electromagnetic wave pattern as shown in the figure below. B E What is the direction in which the wave is traveling? 1. fromlefttoright. 2. undetermined, since the figure shows a standing wave. 3. fromrighttoleft. correct Explanation: The direction of traveling is the direction of vector E vector B ; i.e. , fromrighttoleft. 002 (part 1 of 3) 10.0 points A plane electromagnetic sinusoidal wave of frequency 18 . 7 MHz travels in free space. The speed of light is 2 . 99792 10 8 m / s. Determine the wavelength of the wave. Correct answer: 16 . 0317 m. Explanation: Let : c = 2 . 99792 10 8 m / s , and f = 18 . 7 MHz = 1 . 87 10 7 Hz . The speed of light is c = f = c f = 2 . 99792 10 8 m / s 1 . 87 10 7 Hz = 16 . 0317 m . 003 (part 2 of 3) 10.0 points Find the period of the wave. Correct answer: 5 . 34759 10 8 s. Explanation: The period T of the wave is the inverse of the frequency: T = 1 f = 1 1 . 87 10 7 Hz = 5 . 34759 10 8 s . 004 (part 3 of 3) 10.0 points At some point and some instant, the electric field has has a value of 205 N / C. Calculate the magnitude of the magnetic field at this point and this instant. Correct answer: 6 . 83806 10 7 T. Explanation: Let : E = 205 N / C . The magnitudes of the electric and the mag netic fields are related by E B = c , B = E c = 205 N / C 2 . 99792 10 8 m / s = 6 . 83806 10 7 T . 005 10.0 points The cable is carrying the current I ( t ). Evaluate the electromagnetic energy flux S at the surface of a long transmission cable of resistivity , length and radius a , using the expression vector S = 1 vector E vector B . gonzales (pag757) Homework 12 Hoffmann (56745) 2 1. S = I 2 a 2 2. S = I 2 2 a 2 3. S = I 2 2 2 a 3 correct 4. S = c I 2 4 a 2 5. None of these. 6. S = I 2 a 2 7. S = I 2 a 2 8. S = I 2 4 c 9. S = I 2 2 a 2 10. S = a 2 I 2 Explanation: The basic expression for the Poynting Vec tor is vector S = 1 vector E vector B ....
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 Spring '08
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