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Unformatted text preview: benavides (jjb2356) – homework 25 – Turner – (59130) 1 This print-out should have 11 questions. Multiple-choice 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 out of the paper. The separation between 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 ( z or a ) 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 z > V a (right) and V a > V z (left) 2. V z > V a (right) and V z > V a (left) 3. V z = V a (right) and V z = V a 4. V a > V z (right) and V a > V z (left) correct 5. V a > V z (right) and V z > V a (left) Explanation: As the bar moves toward the resistor, the area of the current loop decreases, so the induced vector B ind is upward with I ind counter- clockwire from above. Lenz’s law dictates that before moving past the resistor, current flows from a to z , so a is at a higher potential. After going past the resistor, Lenz’s law dictates that the induced vector B ind is now down- ward. This requires the current to reverse its ro- tational direction to be clockwise from above. However, the direction a to z (through the resistor R ) also reverses its rotational direc- tion. The emf across the bar does not change sign; i.e. , the current through the resistor R remains in the same direction. 002 10.0 points A rectangular coil of 25 turns, 0 . 17 m by . 26 m, is rotated at 89 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 . 5 V. What is the magnitude of the field? Correct answer: 5 . 08414 mT. Explanation: Let : N = 25 turns , ω = 89 rad / s , ǫ max = 0 . 5 V , x = 0 . 17 m , and y = 0 . 26 m ....
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This note was uploaded on 03/26/2012 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas.
- Spring '08