finalA_key

finalA_key - Final Exam Name: ID: 1. Q1 (-1,0) 2. (10...

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Name: ID: 1. (10 points) In an X-Y coordinate system with unit in meter, charge Q1 of 7.865 μC is placed at (-1,0). Charge Q2 of -7.865 μC is placed at (1,0). A third charge Q3 of charge 1 μC is placed at (0,1), (a) What is the total force on Q3? State the magnitude and direction with respect to the coordinate system. (b) What is the electric field (both magnitude and direction) at point (0,-1)? Coulomb’s constant k = 8.99×10 9 Nm 2 /C 2 . 1. (10 points) A parallel plate capacitor is constructed with two plates separated by 0.01 mm. Each plate has a surface area of 1 m 2 . One plate has charge + 8.85 μC. The other plate has charge -8.85 μC, (a) what is the electric potential difference across the two plates? (b) Now you plan to double the amount of electric potential energy stored in this capacitor by connecting it to a DC power supply, what would be the voltage from this power supply? The permittivity constant ε 0 = 8.85×10 -12 C 2 /Nm 2 . V 10 (V) 10 86 8 10 86 8 (a) 7 6 = × × = = - - . . C Q V (-1,0) (0,-1) (0,1) (1,0) Q1 Q3 Q2 F 13 F 23 F x E x 0.05N (N) 45 cos 2 10 1 10 865 7 10 99 8 2 45 cos 2 0 6 6 9 2 3 1 3 = × × × × × = = = + = - - o o x y y x . . r Q Q k F F , y ˆ F x ˆ F F (a), the force y components cancel; x components add up (b), because the symmetry in arrangement: N/C 10 5 N/C 10 1 05 0 N/C 10 25 2 N/C 2 10 1 10 99 8 4 6 3 2 6 9 2 3 × = × = = × - = × × - = - = + = - - . q / F E . . r Q k E , y ˆ E x ˆ E E test x x y y x μF 885 0 (F) 10 1 1 10 85 8 5 12 0 . . d
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This note was uploaded on 05/06/2008 for the course PHYS 1304 taught by Professor Ye during the Spring '08 term at SMU.

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finalA_key - Final Exam Name: ID: 1. Q1 (-1,0) 2. (10...

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