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Session 20: Induction and Lenz’s Law Supplemental Instruction Iowa State University Leader: Course: Instructor: Date: Garrett Schieber Phys 222 Dr. Al-Saqer 10/20/14 Part 1: Conceptual Quesitons 1) A circular loop of wire is in a region of spatially uniform magnetic field, as shown in the figure. The magnetic field is directed into the plane of the figure. a) Determine the direction of the induced current in the loop when B is increasing. The induced current always wants to oppose the change in flux, so when B is increasing, the circular loop will want to induce a current so that the current creates a B field against the increasing B-field. Thus, the induced current will be Counter Clockwise. b) Determine the direction of the induced current in the loop when B is constant with value B0. 2) Using Lenz's law, determine the direction of the current in resistor ab of the figure when: (Book 29.17) a) Switch S is opened after having been closed for several minutes. When the switch is closed, there is a current in coil A. When the switch opens, the current decreases (to zero), thus the induced current in coil B wants to produce a B-field in the same direction as originally. In order to produce this new B-field, the current must flow through the resistor in the direction from a to b. b) Coil B is brought closer to coil A with the switch closed. c) The resistance of R is decreased while the switch remains closed. See Lenz’s Law Practice worksheet for more problems. Supplemental Instruction 1060 Hixson-Lied Student Success Center 294-6624 www.si.iastate.edu