Name ___________________________________ Student ID _______________ Score______ _____ last first Physics 123A, Spring 2008 Exam 1 WO-UWA123A082T-E1(LNZ) IV. [20 points total] A copper loop is held above a table, as shown at right. There is a non-uniform magnetic field directed upward. The loop is initially parallel to the plane of the table. A. The loop is now released from rest, and begins to fall under gravity. i. [5 pts] While the loop is falling, is the induced current in the loop to the left across the front , to the right across the front, or zero? Explain. Choosing an area vector pointing upward, the flux through the loop is positive. The loop is falling into a region with a stronger magnetic field, so the change in flux is also positive. According to Lenz’ law, the induced flux opposes the change in external flux. In this case, the induced field must point downward inside the loop so that the induced flux is negative.
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