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Unformatted text preview: brown (twb493) ch20-h1 chiu (56565) 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Which of the following statements about the discharging of a capacitor through a light bulb are correct? List all that apply separated by commas. If none are true, type none. A. The fringe field of the capacitor decreases as the charge on the capacitor plates de- creases. B. Electrons flow across the gap between the plates of the capacitor, thus reducing the charge on the capacitor. C. The electric field at a location inside the wire is due to charge on the surface of the wires and charge on the plates of the capacitor. D. Electrons in the wires flow away from the negative plate toward the positive plate, reducing the charge on the plates. Correct answer: A,C,D. Explanation: a) Electric field in a capacitor is propor- tional to the surface charge of the capacitor plate. The more charge in the plate, the more intensity of fringe field. b) This answer is wrong because electron does not flow through the space and reach other plate. c) This answer is correct because electric field obeys superposition principle. Because both wire and surface charge creates an elec- tric field, any points inside the wire will be a combination of electric fields. d) This answer is correct because charges can flow through the wire. 002 (part 1 of 6) 5.0 points A particular capacitor is initially charged. Then a high-resistance Nichrome wire is con- nected between the plates of the capacitor, as shown in Figure 1. The needle of a compass placed under the wire deflects 20 o to the east as soon as the connection is made. After 60 seconds the compass needle no longer deflects. (I) i i i (II) i i i (III) Which of the diagrams in Figure 1 best in- dicates the electron current at three locations in this circuit: 0.01 seconds after the circuit is connected? 1. Figure II 2. Figure III correct 3. Figure I Explanation: The capacitor is discharging, so the electron current decreases exponentially. Thus, the correct diagrams are: 1. (Figure III) 2. (Figure II) 3. (Figure I) 003 (part 2 of 6) 5.0 points 15 seconds after the ciruit is connected?...
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This note was uploaded on 12/01/2011 for the course PHY 303L taught by Professor Turner during the Fall '08 term at University of Texas at Austin.
- Fall '08