HW 14 - terry(ect328 – homework 14 – Turner –(59130 1...

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Unformatted text preview: terry (ect328) – homework 14 – Turner – (59130) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Current is carried throughout the body of a type-II superconductor. Assume: The density of superconducting electrons is 5 × 10 27 m − 3 . If a Nb 3 Sn (type II) superconducting wire of cross sectional area 4 . 1 mm 2 can carry a 1 × 10 5 A supercurrent, what is the average (drift) velocity of the superconducting electrons? Correct answer: 30 . 4497 m / s. Explanation: Let : n = 5 × 10 27 m − 3 , A = 4 . 1 mm 2 = 4 . 1 × 10 − 6 m 2 , and I = 1 × 10 5 A . The drift velocity is v = I q e nA = 1 × 10 5 A (1 . 602 × 10 − 19 C) × 1 (5 × 10 27 m − 3 ) (4 . 1 × 10 − 6 m 2 ) = 30 . 4497 m / s . 002 10.0 points A length of metal wire has a radius of 0 . 004 m and a resistance of 0 . 08 Ω. When the potential difference across the wire is 19 V, the electron drift speed is found to be 0 . 000331 m / s. Based on these data, calculate the density of free electron in the wire. Correct answer: 8 . 92166 × 10 28 m − 3 . Explanation: Let : r = 0 . 004 m , R = 0 . 08 Ω , Δ V = 19 V , and v d = 0 . 000331 m / s . The current in the wire is I = Δ V R = 19 V . 08 Ω = 237 . 5 A . From v d = I nq A , the density of free elec- tron is n = I v d q e ( π r 2 ) = 237 . 5 A (0 . 000331 m / s) (1 . 6 × 10 − 19 C) × 1 π (0 . 004 m) 2 = 8 . 92166 × 10 28 m − 3 . 003 10.0 points At 50 ◦ C, the resistance of a segment of gold wire is 84 Ω. When the wire is placed in a liquid bath, the resistance increases to 167 Ω. The temperature coefficient is 0 . 0034 ( ◦ C) − 1 at 20 ◦ C. What is the temperature of the bath? Correct answer: 370 . 259 ◦ C. Explanation: Let : R 1 = 84 Ω , R 2 = 167 Ω , T = 20 ◦ C , T 1 = 50 ◦ C , and α = 0 . 0034( ◦ C) − 1 ....
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This note was uploaded on 02/17/2010 for the course PHY 59130 taught by Professor Turner during the Fall '09 term at University of Texas.

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HW 14 - terry(ect328 – homework 14 – Turner –(59130 1...

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