solution_pdf14 - tovar(jdt436 – homework 14 – Turner...

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Unformatted text preview: tovar (jdt436) – homework 14 – Turner – (59070) 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 2 . 9 mm 2 can carry a 1 × 10 5 A supercurrent, what is the average (drift) velocity of the superconducting electrons? Correct answer: 43 . 0496 m / s. Explanation: Let : n = 5 × 10 27 m − 3 , A = 2 . 9 mm 2 = 2 . 9 × 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 ) (2 . 9 × 10 − 6 m 2 ) = 43 . 0496 m / s . 002 10.0 points A length of metal wire has a radius of 0 . 005 m and a resistance of 0 . 11 Ω. When the potential difference across the wire is 18 V, the electron drift speed is found to be 0 . 000307 m / s. Based on these data, calculate the density of free electron in the wire. Correct answer: 4 . 24162 × 10 28 m − 3 . Explanation: Let : r = 0 . 005 m , R = 0 . 11 Ω , Δ V = 18 V , and v d = 0 . 000307 m / s . The current in the wire is I = Δ V R = 18 V . 11 Ω = 163 . 636 A . From v d = I nq A , the density of free elec- tron is n = I v d q e ( π r 2 ) = 163 . 636 A (0 . 000307 m / s) (1 . 6 × 10 − 19 C) × 1 π (0 . 005 m) 2 = 4 . 24162 × 10 28 m − 3 . 003 10.0 points At 45 ◦ C, the resistance of a segment of gold wire is 59 Ω. When the wire is placed in a liquid bath, the resistance increases to 183 Ω. The temperature coefficient is 0 . 0034 ( ◦ C) − 1 at 20 ◦ C. What is the temperature of the bath? Correct answer: 715 . 688 ◦ C. Explanation: Let : R 1 = 59 Ω , R 2 = 183 Ω , T = 20 ◦ C , T 1 = 45 ◦ C , and α = 0 . 0034( ◦ C) − 1 ....
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This note was uploaded on 12/11/2009 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas.

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solution_pdf14 - tovar(jdt436 – homework 14 – Turner...

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