exam03_W08-white-solutions

exam03_W08-white-solutions - Exam 2 — white version...

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Unformatted text preview: Exam 2 — white version Physics 2760 SP 2008 Last Name First Name ID# This is a closed book exam. I understand, pursuant to University Regulations on academic honesty, that I am not to use any notes or information other than what is in the official, non—annotated formula sheet. Signature For multiple choice questions, please make sure that you circle the letter for the answer which you believe to be correct and only that answer. If more than one answer is circled for the same problem, you will not receive credit for it. Don’t get hung up on questions. They should take only one or two minutes each. If you find yourself spending more than a few minutes on a multiple choice question you are probably looking at it the wrong way. You should skip it for now and come back to it later. For full credit show your work for solutions to questions that require calculations. Explain from where you start to solve the problem and show your math flowing from it for full credit. No shown work, no credit! Relax, read carefully, think — and then read everything again. During the exam, if you have questions please raise your hand and the TA or the instructor will come to you and provide help. 1. Two loops carry equal currents l in the same direction. The loops are held in the positions shown in the figure and are then released. Which one of the l ' H following statements correctly describes the subsequent behavior of the loops? CED) I l a) Both loops move to the left. b) The loops remain in the positions shown. it c) The top loop moves to the right; the bottom loop moves to the right. Q I l l d The loops repel each other. @ he loops attract each other. Two coils, 1 and 2, with iron cores are positioned as shown in the figure. Coil 1 is part of a circuit with a battery and a switch. ‘ n induced current will flow from right to left in R. b) An induced current will flow from left to right in r. c) A magnetic field that points toward B appears inside coil 1. d) An induced magnetic field that points toward B appears inside coil 2. A e) A current will pass through r, but there will be no current through R. ilmmediately after the switch S is closed, which one of the following statements is true? 075; ‘5 3. Assume that S has been closed for a long time. Which one of the following changes will result in an induced magnetic field in coil 2 that points toward C? a) The switch S is opened. b The iron core is removed from coil 1. @oil 1 and its core are moved toward B. ) Coil 1 and its core are moved toward A. e) Coil 2 and its core are moved toward C. 4. A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, ollows a clockwise spiral of decreasing radius as shown. A reasonable explanation is: a V he charge is positive and slowing down x ‘ B) the charge is negative and slowing down C) the charge is positive and speeding up ~% 4 *3 D) the charge is negative and speeding up “l' 339' X % x E) none ofthe above 5. The figure shows a uniform magnetic field B directed to the left and a wire rrying a current into the page. The magnetic force acting on the wire is: oward the top of the page B) toward the bottom of the page (3)) ttowar: ttlge leftht __>) _)} 1 urrent owar e rIg ; : l x 2 <— <— E) zero 6. Consider a current I = 0.5 A that flows in a plane rectangular current loop with height a = 4.00 cm and horizontal sides b = 2.00 cm. The loop is placed into a uniform magnetic field E of magnitude 3 T, in such a way that the sides of length a are perpendicular to E, and there is an angle 0 = 30° between the sides of length b and E, as shown in the figures. / / b Mlcmml E / é“);ng up) 0L : @607 9 W fidx a / g ’ . o I gogzmn) i? : 04 ; (00 View from the side Wm from above a) Calculate the gnetic moment of the current loop. (7 points) iii): 1- A =>/A.=1'h {LUXQ = max 0.0160303 b) Calculate the net torque of the current loop due to the interaction of the current with the magnetic field. (8 points) ———» c) Calculate the change in potential energy of the coil-magnetic field system when the coil rotates from 0=30° t00=90°.(10 points) . q ,9) g). : 7V (is —= w Ecowk Di: —' C03 606 7. A rectangular coil of width a = 0.2 m and length b = 0.3 m is located in a magnetic field of magnitude B = 0.8 T directed into the page, as shown in the figure. The resistance of the coil is 16 Q. A) Find the magnitude and direction ofthe induced current ifthe coil is moved with a speed of 2 m/s to the right. (5 points) Eu—Qkh >¢=COWA >7 820 X X X X X X om B) Find the magnitude and direction of the induced current ifthe coil is moved with a speed of2 m/s up. (20 points) 8. A long, rigid conductor, lying along the y axis, carries a current of 6 A in the positive y direction. A magnetic field E = 2y2i + 83' (with y in meters and B in Tesla) is present. Find the force (in vector notation) on the 2 m long conductor that lies between y = 1 m and y = 3 m. (25 points) MC 06 Q7 08 Total 25/ 25/ 25/ 25/ 100/ ...
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