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Unformatted text preview: oliver (jmo673) HW05 Tsoi (59090) 1 This printout should have 29 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points The current in a wire decreases with time according to the relationship I = (2 . 14 mA) e a t where a = 0 . 13328 s 1 . Determine the total charge that passes through the wire from t = 0 to the time the current has diminished to zero. Correct answer: 0 . 0160564 C. Explanation: I = dq dt q = integraldisplay t t =0 I dt = integraldisplay t =0 (0 . 00214 A) e . 13328 s 1 t dt = (0 . 00214 A ) e . 13328 s 1 t . 13328 s 1 vextendsingle vextendsingle vextendsingle vextendsingle vextendsingle = . 0160564 C . 002 10.0 points If a metal wire carries a current of 17.0 mA, how long does it take for 9.90 10 20 electrons to pass a given crosssectional area anywhere along the wire? The magnitude of the charge on an electron is 1 . 6 10 19 C. Correct answer: 9317 . 65 s. Explanation: Let : q e = 1 . 6 10 19 C , I = 17 . 10 2 A and N = 9 . 90 10 20 . I = Q t = N q e t t = N q e I = (9 . 9 10 20 )(1 . 6 10 19 C) . 017 A = 9317 . 65 s . 003 (part 1 of 3) 10.0 points A total charge of 18 mC passes through a crosssectional area of a nichrome wire in . 46 s. a) What is the current in the wire? Correct answer: 0 . 0391304 A. Explanation: Let : Q 1 = 18 mC and t 1 = 0 . 46 s . I = Q t = . 018 C . 46 s = . 0391304 A . 004 (part 2 of 3) 10.0 points b) How many electrons pass through the crosssectional area in 38.0 s? Correct answer: 9 . 29348 10 18 . Explanation: Let : q e = 1 . 6 10 19 C and t 2 = 38 . 0 s . Q = N q e N = Q q e = I t 2 q e = (0 . 0391304 A)(38 s) 1 . 6 10 19 C = 9 . 29348 10 18 . 005 (part 3 of 3) 10.0 points c) If the number of charges that pass through the crosssectional area during the given time oliver (jmo673) HW05 Tsoi (59090) 2 interval doubles, what is the resulting cur rent? Correct answer: 0 . 0782609 A. Explanation: Let : Q 2 = 2 Q 1 . I = 2 Q 1 t 1 = 2 (0 . 018 C) . 46 s = . 0782609 A . 006 (part 1 of 2) 10.0 points The current in a conductor varies over time as shown in the figure. 1 2 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 Current(A) Time(s) How much charge passes through a cross section of the conductor in the time interval t = 0 s to t = 2 . 5 s? Correct answer: 9 C. Explanation: Let : t = 2 . 5 s . The charge is the area under the I vs t graph, represented here by two rectangles and two triangles: Q = (2 A)(2 . 5 s) + (6 A 2 A)(0 . 5 s) + 1 2 (6 A 2 A)(0 . 5 s) + 1 2 (6 A 2 A)(0 . 5 s) = 9 C ....
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This note was uploaded on 10/21/2009 for the course PHY 59090 taught by Professor Tsoi during the Fall '09 term at University of Texas.
 Fall '09
 TSOI
 Physics, Current

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