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Unformatted text preview: Manage this Assignment: 5a. Magnetism Due: 11:00pm on Sunday, February 7, 2010 Note: To understand how points are awarded, read your instructor's Grading Policy . Print Version with Answers A Wire and a Compass Description: Short conceptual problem on the deflection of a compass needle placed in proximity to a wire through which a current flows. Based on Young/Geller Conceptual Analysis 20.7. You are looking straight down on a magnetic compass that is lying flat on a table. A wire is stretched horizontally under the table, parallel to and a short distance below the compass needle. The wire is then connected to a battery so that a current flows through the wire. This current causes the north pole of the compass needle to deflect to the left. The questions that follow ask you to compare the effects of different actions on this initial deflection. Part A If the wire is lowered farther from the compass, how does the new angle of deflection of the north pole of the compass needle compare to its initial deflection? As the distance between the wire and the compass increases, the magnetic field produced by the wire weakens. Therefore, the north pole of the compass needle will deflect away from its original direction (determined by Hint A.1 How to approach the problem When the switch is closed, current passes through the wire and a magnetic field is created near the wire. This causes the north pole of the compass needle to deflect. The magnitude of the magnetic field produced by the conductor changes as you move farther away from the conductor. Therefore, when the wire is lowered, the compass needle will detect a different magnetic field. To determine the effect on the angle of deflection, find how the magnetic field's magnitude varies with the distance from the conductor. Hint A.2 Find an expression for the magnetic field's magnitude produced by a conductor Which of the following expressions gives the magnitude of the magnetic field , produced by a conductor carrying a current , at a distance from the axis of the conductor? In the equations below, let denote the permeability of free space. As you discovered, the magnitude of the magnetic field produced by a straight conductor carrying a current decreases with the distance from the conductor. Therefore, what will be the effect on the north pole of the compass needle as the wire is lowered farther away from the compass? ANSWER: ANSWER: It is smaller. Page 1 of 15 MasteringPhysics: Assignment Print View 2/10/2010 http://session.masteringphysics.com/myct/assignmentPrint?assignmentID=1335162 the magnetic field of the earth) by a smaller angle....
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