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Unformatted text preview: Nguyen, Thanh Homework 8 Due: Feb 19 2008, 7:00 pm Inst: Weathers 1 This printout should have 11 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 quantity of charge passing through a sur face of area 1 . 14 cm 2 varies with time as q = q 1 t 3 + q 2 t + q 3 , where q 1 = 2 . 7 C / s 3 , q 2 = 6 . 6 C / s, q 3 = 7 C, and t is in seconds. What is the instantaneous current through the surface at t = 1 s? Correct answer: 14 . 7 A. Explanation: Let : q 1 = 2 . 7 C / s 3 , q 2 = 6 . 6 C / s , q 3 = 7 C , and t = 1 s . I dq dt = 3 q 1 t 2 + q 2 = 3 ( 2 . 7 C / s 3 ) (1 s) 2 + 6 . 6 C / s = 14 . 7 A . 002 (part 2 of 2) 10 points What is the value of the current density at t = 1 s? Correct answer: 128947 A / m 2 . Explanation: Let : a = 1 . 14 cm 2 = 0 . 000114 m 2 and t = 1 s . J I A = 14 . 7 A . 000114 m 2 = 128947 A / m 2 . keywords: 003 (part 1 of 1) 10 points A conductor with crosssectional area 1 cm 2 carries a current of 18 A. If the concentration of free electrons in the conductor is 6 10 28 electrons / m 3 , what is the drift velocity of the electrons? Correct answer: 0 . 0187245 mm / s....
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This note was uploaded on 10/24/2011 for the course PHYS 2220 taught by Professor Littler during the Spring '00 term at North Texas.
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