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# Exam1eq - Physics 21 Fall 2008 1 2 3 4 5 Total Name...

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Physics 21 Fall, 2008 Hour Exam #1 1 2 3 4 5 Total Name: Recitation Time Recitation Leader October 3, 2008 This exam is closed notes and closed book. You must show enough work on each problem to convince the grader you understand how to solve the problem. You may use a calculator, but show every number that you use to get numerical results. The penalty for arithmetic errors is small if the grader can tell what you intended to do. Give units for all final answers. There is an equation sheet on the last page. All problems count 20 points. Problem 1. Consider the following circuit: 2 I 2 32 V 40 V 4 5 I 1 I 3 6 a b c d (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 in 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 a - V d between the points labelled a and d on the di- agram. Use the calculated values of the currents and show how you get your answer.

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Problem 2. A point charge q 1 = - 4 . 00 nC is at the point x = 0 . 20 m, y = 0 . 10 m, and a second point charge q 2 = +6 . 00 nC is at the point x = 0 . 70 m, y = 0 . 30 m. The coordinates of the point P are x = 1 . 00 m, y = 0 . 70 m x y q 1 q 2 P = (1.00,0.7) 1.0 1.0 Distances are in meters. (a) (4 pts.) Give the general formula for the electric field E at any point r due to a charge q at the point r . (b) (4 pts.) Calculate the x and y components of the electric field E 1 at the point P due to charge q 1 . (c) (4 pts.) Calculate the x and y components of the electric field E 2 at the point P due to charge q 2 . (d) (4 pts.) Calculate the x and y components of the net electric field E at the point P due to these two point charges.
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Exam1eq - Physics 21 Fall 2008 1 2 3 4 5 Total Name...

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