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Unformatted text preview: gilvin (jg47854) 20. Lenz and Faradays laws meyers (21235) 1 This printout should have 26 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. This homework is due Tuesday, April 26, at midnight Tucson time. 001 (part 1 of 3) 10.0 points A rectangular loop of copper wire of resis tance R has width a and length b . The loop is stationary in a constant, the magnetic field B at time t = 0 seconds is directed into the page as shown below. The uniform magnetic field varies with time t according to the rela tionship B = B cos t , where and B are positive constants and B is positive when the field is directed into the page. B B B B b a n turns The direction of the induced current in the loop when t = 2 , after the magnetic field begins to oscillate is 1. clockwise. correct 2. undetermined, since the current is zero. 3. counterclockwise. Explanation: When t = 2 , B = B cos 2 = 0; i.e. , the field has been decreasing, and is about to change direction. The induced current will be in a direction to oppose this change; i.e. , clockwise. 002 (part 2 of 3) 10.0 points What is the expression for the magnitude of the induced current in the loop as a function of time in terms of a , b , B , , R , t , and fundamental constants. 1. I = a bB R sin t 2. I = a bB R sin t 3. I = RB a b sin t 4. I = a b B R sin t 5. I = a b B R sin t correct 6. I = R B a b sin t Explanation: Calculating the flux, = a bB cos t. Calculating the emf , E = d dt (negative sign not required) = a b B sin t. Using Ohms Law I = E R = a b B R sin t. 003 (part 3 of 3) 10.0 points Select a sketch a graph of the induced cur rent I vs t , taking clockwise current to be positive. 1. t I 2 3 2 2 5 2 3 gilvin (jg47854) 20. Lenz and Faradays laws meyers (21235) 2 2. t I 2 3 2 2 5 2 3 correct 3. t I 2 3 2 2 5 2 3 4. t I 2 3 2 2 5 2 3 5. t I 2 3 2 2 5 2 3 6. t I 2 3 2 2 5 2 3 Explanation: The graph is a sine wave with period 2 . t I 2 3 2 2 5 2 3 004 10.0 points A coil is wrapped with 382 turns of wire on the perimeter of a circular frame (of radius 62 cm). Each turn has the same area, equal to that of the frame. A uniform magnetic field is directed perpendicular to the plane of the coil. This field changes at a constant rate from 24 mT to 60 mT in 42 ms. What is the magnitude of the induced E in the coil at the instant the magnetic field has a magnitude of 49 mT? Correct answer: 395 . 412 V....
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This note was uploaded on 04/29/2011 for the course PHYS 202 taught by Professor Doc during the Spring '11 term at North Texas.
 Spring '11
 doc
 Magnetism, Work

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