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Unformatted text preview: white (rw22679) Hw03 Ross (10219) 1 This printout should have 14 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points Birds resting on highvoltage power lines are a common sight. The copper wire on which a bird stands is 1 . 34 cm in diameter and carries a current of 95 A. Coppers resistivity is 1 . 68 10 8 m . If the birds feet are 1 . 76 cm apart, what is the potential difference across its body? Correct answer: 199 . 18 V. Explanation: Let : r = 0 . 67 cm = 0 . 0067 m , I = 95 A , L = 1 . 76 cm = 0 . 0176 m , and = 1 . 68 10 8 m . The resistance of the wire between the feet is R = L A so the potential is V = I R = I L A = (95 A) (1 . 68 10 8 m) (0 . 0176 m) (0 . 0067 m) 2 10 6 V V = 199 . 18 V . 002 10.0 points A 17 V battery delivers 119 mA of current when connected to a 72 resistor. Determine the internal resistance of the battery. Correct answer: 70 . 8571 . Explanation: Let : V = 17 V , I = 119 mA = 0 . 119 A , and R = 72 . The internal resistance is in series with the given resistor, so V = I ( R + r ) r = V I R = 17 V . 119 A 72 = 70 . 8571 . 003 (part 1 of 2) 10.0 points A transistor radio operates by means of a 12 V battery that supplies it with 56 mA current. If the cost of the battery is 2 . 01 dollars and it lasts for 317 h, what is the cost per kWh to operate the radio in this manner? Correct answer: 9 . 43556 dollars / kW h. Explanation: Let : V = 12 V , I = 56 mA , c 1 = 2 . 01 dollars , and t = 317 h . The energy is E = P t = ( I V ) t , so the cost per kilowatt hour is c u 1 = c 1 E = c 1 I V t = 2 . 01 dollars (56 mA) (12 V) (317 h) parenleftbigg 1000 mA 1 A parenrightbiggparenleftbigg 1000 W 1 kW parenrightbigg = 9 . 43556 dollars / kW h white (rw22679) Hw03 Ross (10219) 2 004 (part 2 of 2) 10.0 points(part 2 of 2) 10....
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This note was uploaded on 12/01/2010 for the course PHYSICS 21900 taught by Professor Rhoads during the Spring '10 term at IUPUI.
 Spring '10
 Rhoads
 Physics, Power

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