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Unformatted text preview: 1 Physics 4B THIRD EXAM Chapters 22 - 32 Spring 1998 Name:_________________________________________ Solve the following problems in the space provided. Use the back of the page if needed. Each problem is worth 20 points. You must show your work in a logical fashion starting with the correctly applied physical principles which are on the last page. Your score will be maximized if your work is easy to follow because partial credit will be awarded. 1. A 62.0cm long wire has a mass of 130g and is hung horizontally from two conducting springs. The wire is perpendicular to an 0.880T magnetic field directed into the page as shown. Find the magnitude and direction of the current in the wire if the springs are unstretched. According to the right hand rule, the current must be moving toward the right in order to feel an upward force. Starting with Newtons Second Law, F = ma F m- mg = F m = mg . Using the definition of magnetic field I l B = mg I = mg l B = (0.130)(9.80) (0.620)(0.880) I = 2.34A . 2. Find the magnitude and direction of the magnetic field at the center of the coil shown at the right. The coil has 100 turns, a radius of 5.00cm and carries 1.00A of current.The coil has 100 turns, a radius of 5....
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