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SS2005-Exam3

SS2005-Exam3 - PHYSICS 112 SUMMER 2005 EXAM 3 Name...

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PHYSICS 112 - SUMMER 2005 - EXAM 3 Name: _________________________________________ Recitation Section: ______ NO CALCULATORS ALLOWED - BUT, LUCKILY, NO CALCULATORS NEEDED. SHOW YOUR WORK! Full credit will be given only if you explain how you arrived at your answer. Either show your work (especially in a calculation) or give a short explanation. Nothing elaborate is required, but the grader must be able to follow your reasoning clearly. 1. [5 points] A square circuit is shown below. It is located in a uniform magnetic field directed in the direction shown (in the same plane as the circuit). Assume that there is a clockwise current in the circuit. â F t ext (a) [1 point] Determine the direction of the magnetic field of the current on the inside of the circuit, and mark it on the diagram. (b) [2 points] Determine the direction of the magnetic force on each side of the circuit. Mark these on the diagram. (c) [2 points] Determine if there is a net torque on the circuit, and, if so, describe how the circuit will rotate (for example, "clockwise as viewed from below the bottom of the circuit").

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2. [7 points] A square circuit is shown below; it is held so it cannot rotate. Each side has length 0.20 m, and the total resistance of the circuit is 4.0 . It is located in a uniform H magnetic field of magnitude 0.30 T directed in the direction shown (in the same plane as the circuit). Assume that the direction of the magnetic field changes smoothly over a period of 3.0 seconds through a 90° angle until it is directed up ( ). â F t ext
3. [8 points] Remember the demonstration of the magnet dropping slowly through a long vertical aluminum tube? Assuming that the magnet is dropping south-pole down, give a careful explanation of why the currents induced below the falling magnet and above the falling magnet both produce upward forces on the magnet. Make reference to (1) the direction of the magnetic field at the location of these currents, (2) whether the field is increasing or decreasing, and (3) the direction of the magnetic field of the currents.

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