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Unformatted text preview: pan (zp695) Ch21-h2 chiu (56565) 1 This print-out should have 29 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points A current-carrying wire is oriented along the y axis. It passes through a region 0 . 4 m long in which there is a magnetic field of 4 . 1 T in the + z direction. The wire experiences a force of 15 . 5 N in the- x direction. What is the magnitude of the conventional current in the wire? Correct answer: 9 . 45122 A. Explanation: We can find the current as follows: | F | = I L B = I L B I = F L B = 15 . 5 N (0 . 4 m)(4 . 1 T) = 9 . 45122 A . 002 (part 2 of 2) 10.0 points What is the direction of the conventional cur- rent in the wire? 1.- 1 , , 2. , , 1 3. 1 , , 4. , 1 , 5. ,- 1 , correct 6. , ,- 1 Explanation: Use the right-hand rule. The current flows in the- y direction. 003 (part 1 of 3) 10.0 points A metal rod of length 12 cm and mass 65 g has metal loops at both ends, which go around two metal poles as in the following figure. 12 cm 4 cm I = 4 A I = 4 A 70 gram rod I = 4 A The rod is in good electrical contact with the poles but can slide freely up and down. The metal poles are connected by wires to a battery, and a 4 A current flows through the region of the rod. An external magnetic field B is present in the region, large enough that you can neglect the magnetic fields due to the 4 A current. The magnetic field is oriented so as to have the maximum e ff ect on the rod. The rod sits at rest 4 cm above the table. Take the + x axis to be toward the right, the + y axis to be upward, and the + z axis out of the plane of the page. What is the (external) magnetic field in the region of the rod? Begin by finding the x component, B x . If necessary, use g = 9 . 8 m / s 2 . Correct answer: 0 T. Explanation: The metal rod is in equilibrium, so F net = 0. The gravitational force by Earth on the rod is downward, so the magnetic force by the magnetic field on the rod must be upward. Since F mag = I L B and I flows in the + x direction, B must be in the- z direction. Therefore we can immediately tell that the x and y components of the magnetic field are zero. 004 (part 2 of 3) 10.0 points Find B y . Correct answer: 0 T. Explanation: See the explanation for part 1. pan (zp695) Ch21-h2 chiu (56565) 2 005 (part 3 of 3) 10.0 points Find B z . Correct answer: 1 . 32708 T. Explanation: Based on what we discussed in part 1, we can apply the Momentum Principle to find F net = 0 F mag + F grav = 0 F mag = F grav I L B = m g B = m g I L = (65 g)(9 . 8 m / s 2 ) (4 A)(12 cm) = 1 . 32708 T . 006 (part 1 of 9) 10.0 points An electron travels with velocity 5 10 5 , , m / s ....
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This note was uploaded on 02/21/2012 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
- Spring '08