solution3_pdf - white(rw22679 Hw03 Ross(10219 This...

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white (rw22679) – Hw03 – Ross – (10219) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Birds resting on high-voltage 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. Copper’s resistivity is 1 . 68 × 10 - 8 Ω m . If the bird’s feet are 1 . 76 cm apart, what is the potential difference across its body? Correct answer: 199 . 18 μ V. Explanation: Let : r = 0 . 67 cm = 0 . 0067 m , I = 95 A , L = 1 . 76 cm = 0 . 0176 m , and ρ = 1 . 68 × 10 - 8 Ω m . The resistance of the wire between the feet is R = ρ L A so the potential is Δ V = I R = I ρ L A = (95 A) (1 . 68 × 10 - 8 Ω m) (0 . 0176 m) π (0 . 0067 m) 2 × 10 6 μ V V = 199 . 18 μ V . 002 10.0 points A 17 V battery delivers 119 mA of current when connected to a 72 Ω resistor. Determine the internal resistance of the battery. Correct answer: 70 . 8571 Ω. Explanation: Let : V = 17 V , I = 119 mA = 0 . 119 A , and R = 72 Ω . The internal resistance is in series with the given resistor, so V = I ( R + r ) r = V I - R = 17 V 0 . 119 A - 72 Ω = 70 . 8571 Ω . 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
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white (rw22679) – Hw03 – Ross – (10219) 2 004 (part 2 of 2) 10.0 points The same radio, by means of a converter, is
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