HW5-Solutions

# HW5-Solutions - Version PREVIEW HW5 feng (58230) This...

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Version PREVIEW – HW5 – feng – (58230) 1 This print-out should have 19 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices before answering. Concept 23 E08 001 10.0 points Does more current ±ow out of a battery than into it? Does more current ±ow into a light bulb than out of it? 1. More for both 2. The same for both correct 3. more; less 4. Less for both 5. less; more Explanation: Current ±ows through electrical devices just as water ±ows through a plumbing cir- cuit of pipes – the same ±ow on both sides. Holt SF 19A 03 002 10.0 points If a metal wire carries a current of 69.0 mA, how long does it take for 2.30 × 10 20 electrons to pass a given cross-sectional area anywhere along the wire? The magnitude of the charge on an electron is 1 . 6 × 10 19 C. Correct answer: 533 . 333 s. Explanation: Let : q e = 1 . 6 × 10 19 C , I = 69 . 0 × 10 2 A and N = 2 . 30 × 10 20 . I = Δ Q Δ t = N q e Δ t Δ t = N q e I = (2 . 3 × 10 20 )(1 . 6 × 10 19 C) 0 . 069 A = 533 . 333 s . Holt SF 19Rev 58 003 (part 1 of 2) 10.0 points The current in a conductor varies over time as shown in the Fgure below. 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 Current(A) Time(s) a) How much charge passes through a cross section of the conductor in the time interval t = 0 s to t = 4 s? Correct answer: 15 C. Explanation: Let : Δ t = 4 . 0 s . I = Δ Q Δ t Δ Q = I Δ t = (2 A)(1 . 5 s) + (4 A)(1 s) + (6 A)(1 s) + (4 A)(0 . 5 s) = 15 C . 004 (part 2 of 2) 10.0 points b) What constant current would transport the same total charge during the 4 s interval as does the actual current? Correct answer: 3 . 75 A. Explanation: I = Δ Q Δ t = 15 C 4 s = 3 . 75 A . Drift Velocity of Electrons

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Version PREVIEW – HW5 – feng – (58230) 2 005 10.0 points A conductor with cross-sectional area 5 cm 2 carries a current of 10 A. If the concentration of free electrons in the conductor is 8 × 10 28 electrons / m 3 , what is the drift velocity of the electrons? Correct answer: 0 . 00156038 mm / s. Explanation: Let : I = 10 A , n = 8 × 10 28 electrons / m 3 , q e = 1 . 60218 × 10 19 C , and A = 5 cm 2 = 0 . 0005 m 2 .
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## This note was uploaded on 03/07/2010 for the course PHYS 303L taught by Professor Sd during the Spring '10 term at University of Texas.

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HW5-Solutions - Version PREVIEW HW5 feng (58230) This...

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