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Unformatted text preview: Kapoor (mk9499) oldmidterm 02 Turner (60230) 1 This printout should have 21 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points A capacitor network is shown in the following figure. 18 . 2 V 4 . 44 F 5 . 5 F 13 . 6 F a b What is the voltage across the 5 . 5 F upper righthand capacitor? Correct answer: 8 . 12958 V. Explanation: Let : C 1 = 4 . 44 F , C 2 = 5 . 5 F , C 3 = 13 . 6 F , and V = 18 . 2 V . Since C 1 and C 2 are in series they carry the same charge C 1 V 1 = C 2 V 2 , and their voltages add up to V , voltage of the battery V 1 + V 2 = V C 2 V 2 C 1 + V 2 = V C 2 V 2 + C 1 V 2 = V C 1 V 2 = V C 1 C 1 + C 2 = (18 . 2 V)(4 . 44 F) 4 . 44 F + 5 . 5 F = 8 . 12958 V . 002 (part 1 of 2) 10.0 points A coaxial cable with length has an inner conductor that has a radius a and carries a charge of Q . The surrounding conductor has an inner radius b and a charge of Q . Assume the region between the conductors is air. The linear charge density Q . radius = a + Q radius = b Q b What is the electric field halfway between the conductors? 1. E = r 2 2. E = 2 r 2 3. E = Q r 4. E = Q 4 r 5. E = Q r 2 6. E = r 7. E = 4 r 8. E = Q 2 r 2 9. E = Q 2 r 10. E = 2 r correct Explanation: The electric field of a cylindrical capacitor is given by E = 2 r . Kapoor (mk9499) oldmidterm 02 Turner (60230) 2 003 (part 2 of 2) 10.0 points What is the capacitance C of this coaxial cable? 1. C = 2 k e ln parenleftBig a b parenrightBig 2. C = 2 k e ln parenleftbigg b a parenrightbigg correct 3. C = k e ln parenleftbigg b a parenrightbigg 4. C = 2 k e ln parenleftbigg b a parenrightbigg 5. C = k e ln parenleftbigg b a parenrightbigg 6. C = k e ln parenleftBig a b parenrightBig 7. C = k e 8. C = k e 2 ln parenleftbigg b a parenrightbigg 9. C = 2 k e 10. C = a 2 k e b Explanation: C = 2 k e ln parenleftbigg b a parenrightbigg . 004 (part 1 of 4) 10.0 points Four capacitors are connected as shown in the figure. 1 7 . 5 F 55 . 3 F 33 . 1 F 7 3 . 1 F 93 . 4 V a b c d Find the capacitance between points a and b of the entire capacitor network. Correct answer: 111 . 306 F. Explanation: Let : C 1 = 17 . 5 F , C 2 = 33 . 1 F , C 3 = 55 . 3 F , C 4 = 73 . 1 F , and E = 93 . 4 V . C 1 C 3 C 2 C 4 E a b c d A good rule of thumb is to eliminate junc tions connected by zero capacitance. C 2 C 3 C 1 C 4 a b The definition of capacitance is C Q V . The series connection of C 2 and C 3 gives the equivalent capacitance C 23 = 1 1 C 2 + 1 C 3 = C 2 C 3 C 2 + C 3 Kapoor (mk9499) oldmidterm 02 Turner (60230) 3 = (33 . 1 F) (55 . 3 F) 33 . 1 F + 55 . 3 F = 20 . 7062 F ....
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 Fall '08
 Turner
 Physics, Work

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