# HW 14 - benavides(jjb2356 homework 14 Turner(59130 This...

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benavides (jjb2356) – homework 14 – Turner – (59130) 1 This print-out should have 11 questions. Multiple-choice questions may continue on the next column or page – fnd 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 . 4 mm 2 can carry a 1 × 10 5 A supercurrent, what is the average (driFt) velocity oF the superconducting electrons? Correct answer: 28 . 3736 m / s. Explanation: Let : n = 5 × 10 27 m 3 , A = 4 . 4 mm 2 = 4 . 4 × 10 6 m 2 , and I = 1 × 10 5 A . The driFt velocity is v = I q e n A = 1 × 10 5 A (1 . 602 × 10 19 C) × 1 (5 × 10 27 m 3 ) (4 . 4 × 10 6 m 2 ) = 28 . 3736 m / s . 002 10.0 points A length oF metal wire has a radius oF 0 . 005 m and a resistance oF 0 . 05 Ω. When the potential di±erence across the wire is 18 V, the electron driFt speed is Found to be 0 . 00039 m / s. Based on these data, calculate the density oF Free electron in the wire. Correct answer: 7 . 34561 × 10 28 m 3 . Explanation: Let : r = 0 . 005 m , R = 0 . 05 Ω , Δ V = 18 V , and v d = 0 . 00039 m / s . The current in the wire is I = Δ V R = 18 V 0 . 05 Ω = 360 A . ²rom v d = I n q A , the density oF Free elec- tron is n = I v d q e ( π r 2 ) = 360 A (0 . 00039 m / s) (1 . 6 × 10 19 C) × 1 π (0 . 005 m) 2 = 7 . 34561 × 10 28 m 3 . 003 10.0 points At 25 C, the resistance oF a segment oF gold wire is 76 Ω. When the wire is placed in a liquid bath, the resistance increases to 175 Ω. The temperature coe³cient is 0 . 0034 ( C) 1 at 20 C. What is the temperature oF the bath? Correct answer: 414 . 64 C. Explanation: Let : R 1 = 76 Ω , R 2 = 175 Ω , T 0 = 20 C , T 1 = 25 C , and α = 0 . 0034( C) 1 . Neglecting change in the shape oF the wire, we have R 1 = R 0 [1 + α ( T 1 - T 0 )] R 0 = R 1 1 + α ( T 1 - T 0 ) and R 2 = R 0 [1 + α ( T 2 - T 0 )] , where T 0 = 20 C .

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## This note was uploaded on 03/26/2012 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas.

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HW 14 - benavides(jjb2356 homework 14 Turner(59130 This...

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