su09EII

# su09EII - Physics 54 Summer 2009 Exam II Solutions In...

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Physics 54 Summer 2009 1 Exam II Solutions In questions or problems not requiring numerical answers, express the answers in terms of the symbols given and standard constants. If numbers are required, use g = 10 , k = 1/ 4 !" 0 = 9 # 10 9 and μ 0 = 4 ! " 10 # 7 (all in SI units). Part A: Check the best answer. Each question carries a value of 4 points. 1. Which is NOT true of the static magnetic field? Its field lines always form closed curves. On a positive charge it exerts a force along the field lines. [Perpendicular] It exerts no force on a charge at rest. Its field lines near a straight wire carrying current are circles around the wire. 2. Shown is a pair of parallel straight wires carrying equal currents into and out of the page. Which of the following is NOT true of the B-field created by these wires at points in the plane of the page? There is no point at a finite distance where the field is zero. At points between the wires the field is directed downward. At points to the left of both wires the field is directed downward. [Up] At points to the right of both wires the field is directed upward. 3. A small loop of wire is in a non-uniform B-field, with the plane of the loop perpendicular to the field. The strength of the field is increasing with time. The magnetic moment of the current induced in the loop is parallel to the field. [Opposite] The loop experiences a force toward the region of stronger field. The loop experiences a force away from the region of stronger field. The loop experiences no net force. In Out

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Physics 54 Summer 2009 2 4. In the situation shown from above, a bar magnet is rotating counter-clockwise as shown at a small distance above a conducting disk which is free to rotate about an axle through its center. The disk does not rotate. The disk rotates clockwise. The disk rotates counter-clockwise. The disk rotates only if it made of a ferromagnetic material such as iron. [The forces on the disk oppose relative motion, so they drag the disk along with the magnet.] Part B: Check the correct answer. Each question carries a value of 3 points. 5.
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## This note was uploaded on 10/19/2011 for the course PHYSICS 54L taught by Professor Thomas during the Summer '09 term at Duke.

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su09EII - Physics 54 Summer 2009 Exam II Solutions In...

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