ohw 12-solutions

# ohw 12-solutions - howard(cah3459 ohw 12 turner(56705 This...

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howard (cah3459) – ohw 12 – turner – (56705) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 of 3) 10.0 points A total charge oF 6.4 mC passes through a cross-sectional area oF a nichrome wire in 3 . 1 s. a) What is the current in the wire? Correct answer: 0 . 00206452 A. Explanation: Let : Δ Q 1 =6 . 4 mC and Δ t 1 =3 . 1s . I = Δ Q Δ t = 0 . 0064 C 3 . 1s = 0 . 00206452 A . 002 (part 2 of 3) 10.0 points b) How many electrons pass through the cross-sectional area in 40.0 s? Correct answer: 5 . 16129 × 10 17 . Explanation: Let : q e =1 . 6 × 10 - 19 C and Δ t 2 = 40 . 0s . Δ Q = Nq e N = Δ Q q e = I Δ t 2 q e = (0 . 00206452 A)(40 s) 1 . 6 × 10 - 19 C = 5 . 16129 × 10 17 . 003 (part 3 of 3) 10.0 points c) IF the number oF charges that pass through the cross-sectional area during the given time interval doubles, what is the resulting cur- rent? Correct answer: 0 . 00412903 A. Explanation: Let : Δ Q 2 = 2 Δ Q 1 . I = 2 Δ Q 1 Δ t 1 = 2 (0 . 0064 C) 3 . 1s = 0 . 00412903 A . 004 10.0 points An electrician fnds that a 0 . 4 m length oF a certain type oF wire has a resistance oF 0 . 28 Ω. What is the total resistance oF the 84 m oF this wire he plans to use to wire a house? Correct answer: 58 . 8 Ω. Explanation: Let : ± 1 =0 . 4m , ± 2 = 84 m , and R =0 . 28 Ω . A0 . 4 m length oF the wire has a resistance oF λ = R ± 1 , so the total resistance oF the wire is R tot = λ± = R ± 1 ± = ± 0 . 28 Ω 0 . 4m ² (84 m) = 58 . 8 Ω . 005 (part 1 of 2) 10.0 points Suppose that a uniForm wire oF resistance R is stretched uniFormly to N times its original length. Assume the total volume oF the wire re- mains the same, and the volume is given by the product oF the cross sectional area and the length. Denote the original area by A and the area aFter the stretch by A ± .

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howard (cah3459) – ohw 12 – turner – (56705) 2 The ratio A ± A is 1. A ± A = 1 N 2. A ± A = 1 N 2 / 3 3. A ± A = N 4. A ± A = N 2 5. A ± A = 1 N 2 6. A
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## This note was uploaded on 10/11/2010 for the course PHY 56715 taught by Professor Turner during the Spring '10 term at University of Texas.

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ohw 12-solutions - howard(cah3459 ohw 12 turner(56705 This...

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