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Unformatted text preview: Anderson, Matthew Homework 7 Due: Mar 11 2008, noon Inst: Vitaly 1 This printout should have 12 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. The due time is Central time. 001 (part 1 of 2) 10 points The potential difference in a simple circuit is 2 V and the resistance is 3 . What current I flows in the circuit? Correct answer: 0 . 666667 A. Explanation: Let : V = 2 V and R = 3 . The current is I = V R = 2 V 3 = . 666667 A . 002 (part 2 of 2) 10 points How many electrons pass a given point in the circuit in 8 min? Correct answer: 2 10 21 . Explanation: Let : I = 0 . 666667 A , t = 8 min = 480 s , and q e = 1 . 6 10 19 C . I = q t , where q isincoulombsand t inseconds; that is, q = I t, and the total charge for n electrons is q = n q e , so n = q q e = I t q e = (0 . 666667 A)(480 s) 1 . 6 10 19 C = 2 10 21 . keywords: 003 (part 1 of 1) 10 points Birds resting on highvoltage power lines are a common sight. The copper wire on which a bird stands is 1 . 75 cm in diameter and carries a current of 5 A. Coppers resistivity is 1 . 68 10 8 m . If the birds feet are 1 . 25 cm apart, what is the potential difference across its body? Correct answer: 4 . 36539 V. Explanation: Let : r = 0 . 875 cm = 0 . 00875 m , I = 5 A , L = 1 . 25 cm = 0 . 0125 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 = (5 A)(1 . 68 10 8 m)(0 . 0125 m) (0 . 00875 m) 2 10 6 V V = 4 . 36539 V ....
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 Spring '08
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