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Unformatted text preview: Version 034/AACAC midterm 02 Turner (59130) 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A parallelplate capacitor has 2 . 03 cm 2 plates that are separated by 5 . 74 mm with air be tween them. The permittivity of a vacuum is 8 . 85419 10 12 C 2 / N m 2 . If a 5 . 7 V battery is connected to this ca pacitor, how much energy does it store? 1. 2.43599e11 2. 1.91821e11 3. 1.07309e11 4. 1.00126e10 5. 1.42845e11 6. 5.36657e12 7. 2.47153e11 8. 1.16781e11 9. 1.81619e11 10. 5.08689e12 Correct answer: 5 . 08689 10 12 J. Explanation: Let : A = 2 . 03 cm 2 = 0 . 000203 m 2 , d = 5 . 74 mm = 0 . 00574 m , V = 5 . 7 V , and = 8 . 85419 10 12 C 2 / N m 2 . The capacitance is C = A d , and the stored energy is W = 1 2 C V 2 = A V 2 2 d = (8 . 85419 10 12 C 2 / N m 2 ) (0 . 000203 m 2 ) (5 . 7 V) 2 2 (0 . 00574 m) = 5 . 08689 10 12 J . 002 (part 1 of 2) 10.0 points Consider the system of capacitors connected to a battery as shown below. E B 3 F 3 F 3 F 3 F 3 F 3 F Find the equivalent capacitance of the cir cuit. 1. C = 4 3 F 2. C = 3 2 F 3. C = 2 F correct 4. C = 4 F 5. C = 2 3 F 6. C = 3 F 7. C = 1 F Explanation: E B C 1 C 2 C 3 C 4 C 5 C 6 c a b c d Let : C 1 = C = 3 F , Version 034/AACAC midterm 02 Turner (59130) 2 C 2 = C = 3 F , C 3 = C = 3 F , C 4 = C = 3 F , C 5 = C = 3 F , C 6 = C = 3 F , and E B = 6 V . The basic formulae are C eq = 1 1 C 1 + 1 C 2 , connected in series; C 1 + C 2 , connected parallel. So the equivalent capacitance is C ad = 1 1 C + C + 1 C + C + 1 C + C = 1 1 2 C + 1 2 C + 1 2 C = 2 3 C = 2 3 (3 F) = 2 F . 003 (part 2 of 2) 10.0 points What potential difference E B must be ap plied across the capacitor network so that the charge on each plate of each capacitor will have magnitude of 6 C? 1. V ad = 4 3 V 2. V ad = 3 2 V 3. V ad = 3 V 4. V ad = 8 V 5. V ad = 2 3 V 6. V ad = 4 V 7. V ad = 2 V 8. V ad = 6 V correct Explanation: Let : Q = 6 C . Regard the system as an equivalent capacitor with the capacitance C ad = 2 F. The charge on each parallel set of capacitors is the sum of the charges on each of the capacitors ( i.e. , Q 12 = Q 34 = Q 56 = 12 C). The charge on a series set of capacitors is the same ( i.e. , Q total = 12 C). Thus the potential difference between a and d is V ad = Q total C ad = 12 C 2 F = 6 V . 004 10.0 points Consider an RC circuit i C R S E where a battery, a resistor and a capacitor are in series. As the switch is closed, at any instant the current at any part of the circuit is the same. Set the time when we close the switch to t = 0....
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 Fall '09
 Turner

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