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Unformatted text preview: tovar (jdt436) – homework 25 – Turner – (59070) 1 This printout should have 11 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points In the arrangement shown in the figure, the resistor is R and a B magnetic field is directed into the paper. The separation be tween the rails is ℓ . Neglect the mass m of the bar. Assume the bar and rails have negligible resistance and friction. An applied force moves the bar to the left at a constant speed of v . m v R B B ℓ a z What is the relationship between the elec tric potential at the ends of the resistor ( a or z ) while the bar is moving on the “right” side of the resistor (towards the resistor) and mov ing on the “left” side of the resistor (after the bar moves past the resistor)? 1. V a = V z (right) and V a = V z 2. V z > V a (right) and V z > V a (left) correct 3. V a > V z (right) and V z > V a (left) 4. V a > V z (right) and V a > V z (left) 5. V z > V a (right) and V a > V z (left) Explanation: As the bar moves toward the resistor, the area of the current loop decreases, so the in duced vector B ind is downward with I ind clockwise from above. Lenz’s law dictates that before moving past the resistor, current flows from z to a , so z is at a higher potential. After going past the resistor, Lenz’s law dictates that the induced vector B ind is now upward. This requires the current to reverse its rota tional direction to be counterclockwire from above. However, the direction z to a (through the resistor R ) also reverses its rotational di rection. The emf across the bar does not change sign; i.e. , the current through the re sistor R remains in the same direction. 002 10.0 points A rectangular coil of 64 turns, 0 . 12 m by . 28 m, is rotated at 77 rad / s in a magnetic field so that the axis of rotation is perpendicu lar to the direction of the field. The maximum emf induced in the coil is 0 . 4 V. What is the magnitude of the field? Correct answer: 2 . 41574 mT. Explanation: Let : N = 64 turns , ω = 77 rad / s , ǫ max = 0 . 4 V , x = 0 . 12 m , and y = 0 . 28 m ....
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This note was uploaded on 12/11/2009 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
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