Test3 - Husain, Zeena Homework 7 Due: Mar 8 2004, 4:00 am...

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Unformatted text preview: Husain, Zeena Homework 7 Due: Mar 8 2004, 4:00 am Inst: Sonia Paban 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page find all choices before making your selection. The due time is Central time. 001 (part 1 of 2) 10 points A 14 m long piece of wire of density 8 . 34 g / m 3 has a diameter of 12 . 208 mm. The resistiv- ity of the wire is 1 . 7 10- 8 m at 20 C. The temperature coefficient for the wire is . 0038 ( C)- 1 . Calculate the resistance of the wire at 20 C. Correct answer: 0 . 00203328 . Explanation: Given: L = 14 m , r = 6 . 104 mm = 0 . 006104 m , and 20 = 1 . 7 10- 8 m . The area is A = r 2 and the resistance is R = 20 L A = 20 L r 2 = (1 . 7 10- 8 m) 14 m (0 . 006104 m) 2 = . 00203328 . 002 (part 2 of 2) 10 points Calculate the difference in the resistance of the wire between 42 C and 71 C. Correct answer: 0 . 000224068 . Explanation: Given : T 1 = 42 C , T 2 = 71 C , r = 6 . 104 mm = 0 . 006104 m , 20 = 1 . 7 10- 8 m , = 0 . 0038 ( C)- 1 , and L = 14 m . A = r 2 , and 1 = 20 { 1 . 0 + [ T 1- T 20 ] } = (1 . 7 10- 8 m) { 1 . 0 + [0 . 0038 ( C)- 1 ] [(42 C)- (20 C)] } = 1 . 84212 10- 8 m . R 1 = 1 L A = 1 L r 2 = (1 . 84212 10- 8 m) 14 m (0 . 006104 m) 2 = 0 . 00220327 . 2 = 20 { 1 . 0 + [ T 2- T 20 ] } = (1 . 7 10- 8 m) { 1 . 0 + [0 . 0038 ( C)- 1 ] [(71 C)- (20 C)] } = 2 . 02946 10- 8 m . R 2 = 2 L A = 2 L r 2 = (2 . 02946 10- 8 m) 14 m (0 . 006104 m) 2 = 0 . 00242733 . So the difference in the resistance is R = | R 2- R 1 | = | . 00242733 - . 00220327 | = . 000224068 . 003 (part 1 of 1) 10 points Given: A copper bar has a constant velocity in the plane of the paper and perpendicular to a magnetic field pointed into the plane of the paper. Husain, Zeena Homework 7 Due: Mar 8 2004, 4:00 am Inst: Sonia Paban 2 B B-- + + If the top of the bar becomes negative rel- ative to the bottom of the bar, what is the direction of the velocity ~v of the bar? 1. from right to left ( ) correct 2. from left to right ( ) 3. from top to bottom ( ) 4. from bottom to top ( ) Explanation: Positive charges will move in the direction of the magnetic force, while negative charges move in the opposite direction. To produce the indicated charge separa- tion, the positive charges in the conductor ex- perience downward magnetic forces while the negative charges in the conductor experience upward magnetic forces leaving the charge separation show in the figure....
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This note was uploaded on 04/07/2008 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.

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Test3 - Husain, Zeena Homework 7 Due: Mar 8 2004, 4:00 am...

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