115Aex2win08verBsol - Name...

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Unformatted text preview: Name ___________________________________ Student ID Number ____________ last first I. Point Charges. Two point charges are fixed in place at points O and R as shown. The magnitude of Q = 4 . 00 C. The points labeled P and S are just locations (no charge). There are no other electrically charged objects nearby, and the dotted lines indicate horizontal and vertical directions. S O -Q P R +2Q 50 . 0 cm 35 . 0 cm 35 . 0 cm Ignore gravity in this problem. 1. (3 pts) Which choice best represents the direction of the electric force exerted on the charge at R by the charge at O? A B C D E 2. (5 pts) Which choice best represents the magnitude of this force? 4 . 6 N 2 . 2 x 10-1 N 1 . 2 N 5 . 9 x 10-1 N 2 . 9 x 10 5 N A B C D E Now a third charge of value +Q/2 is brought in from a long distance and fixed in place at point S . 3. (5 pts) Which choice best represents the total electric potential energy of these three charges? -0 . 21 J +0 . 21 J -0 . 78 J +0 . 78 J -1 . 4 J A B C D E Physics 115A, Winter 2008, Version B Exam 2, page 1 Name ___________________________________ Student ID Number ____________ last first S +Q/2 I. continued: The figure shows the situation with all three charges fixed in place. Recall that Q = 4 . 00 C. 4. (5 pts) Which choice best represents the magnitude of total electric field strength E at point P due to the three charges? 1 . 82 x 10 6 N/C 1 . 89 x 10 6 N/C 1 . 85 x 10 6 N/C 9 . 29 x 10 5 N/C 9 . 09 x 10 5 N/C A B C D E Actually there is a slight error here. the answer should be 9.16 not 9.09 However, E is the closest choice Use vector components 5. (5 pts) Which choice best represents the electric potential at point P due to the three charges? Assume that the electric potential is zero at an infinite distance from point O. 1 . 83 10 5 V 1 . 14 10 5 V 1 . 39 10 5 V 1 . 55 10 5 V 1 . 67 10 5 V A B C D E R +2Q 50 . 0 cm O -Q P 35 . 0 cm 35 . 0 cm Again the correct answer is 1.32, not 1.39, but C is closest Potential is not a vector Physics 115A, Winter 2008, Version B Exam 2, page 2 Name ___________________________________ Student ID Number ____________ last first P 10 20 30 40 (cm) (cm) 20 10 R S W II. B. Uniform Electric Field. Uniform Electric Field....
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115Aex2win08verBsol - Name...

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