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Unformatted text preview: Physics 21 Fall, 2009 Solution to Hour Exam #1 The graders for the problems were: 1 Belony, 2 Malenda, 3 Drake, 4 Beels, 5 Lyu For questions about the grading, see the grader by Oct. 21. Problem 1. Consider the following circuit: 2 I 1 15 V 7 V 5 3 I 2 I 3 a b loop 1 loop 2 (a) (12 pts.) Write the loop and junction equations needed to determine the currents I 1 , I 2 , and I 3 . You should have three equations for three un- knowns. Indicate clearly the loop used to determine each loop equation. (b) (4 pts.) Determine the currents I 1 , I 2 , and I 3 (including the correct sign) by explicit solution of the equations. You must show your work. (c) (4 pts.) Find the potential difference V b V a between the points labelled b and a on the di- agram. Use the calculated values of the currents and show how you get your answer. Problem 2. The thin rod shown in the diagram ex- tends along the x axis from x = 0 to x = a . There is a uniform linear charge density on the rod. x y P = (0, y ,0) +a x' dQ r- r ' (a) (3 pts.) On the diagram above, draw the vector ( r r ) from the charge dQ on the rod at x = x to...
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