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Unformatted text preview: 4/8/08 8:32 PM MasteringPhysics Page 1 of 12 http://session.masteringphysics.com/myct Assignment Display Mode: View Printable Answers Physics 202 Assignment 9 Due at 11:00pm on Sunday, April 6, 2008 View Grading Details Faraday's Law and Induced Emf Description: Discusses Faraday's law; presents a sequence of questions related to finding the induced emf under different circumstances. Learning Goal: To understand the terms in Faraday's law and to be able to identify the magnitude and direction of induced emf. Faraday's law states that induced emf is directly proportional to the time rate of change of magnetic flux. Mathematically, it can be written as , where is the emf induced in a closed loop, and is the rate of change of the magnetic flux through a surface bounded by the loop. For uniform magnetic fields the magnetic flux is given by , where is the angle between the magnetic field and the normal to the surface of area . To find the direction of the induced emf, one can use Lenz's law: The induced current's magnetic field opposes the change in the magnetic flux that induced the current. For example, if the magnetic flux through a loop increases , the induced magnetic field is directed opposite to the "parent" magnetic field, thus countering the increase in flux. If the flux decreases , the induced current's magnetic field has the same direction as the parent magnetic field, thus countering the decrease in flux. Recall that to relate the direction of the electric current and its magnetic field, you can use the right-hand rule : When the fingers on your right hand are curled in the direction of the current in a loop, your thumb gives the direction of the magnetic field generated by this current. In this problem, we will consider a rectangular loop of wire with sides and placed in a region where a uniform magnetic field exists (see the diagram). The resistance of the loop is . Initially, the field is perpendicular to the plane of the loop and is directed out of the page. The loop can rotate about either the vertical or horizontal axis, passing through the midpoints of the opposite sides, as shown. Part A Which of the following changes would induce an electromotive force (emf) in the loop? When you consider each option, assume that no other changes occur. Check all that apply. ANSWER: The magnitude of increases. The magnitude of decreases. The loop rotates about the vertical axis (vertical dotted line) shown in the diagram. The loop rotates about the horizontal axis (horizontal dotted line) shown in the diagram. The loop moves to the right while remaining in the plane of the page. The loop moves toward you, out of the page, while remaining parallel to itself. 4/8/08 8:32 PM MasteringPhysics Page 2 of 12 http://session.masteringphysics.com/myct Part B Find the flux through the loop....
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