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Unformatted text preview: mcconnell (kam2342) – 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. 17 . 5 V 3 . 81 μ F 6 . 9 μ F 13 . 1 μ F a b What is the voltage across the 6 . 9 μ F upper righthand capacitor? Correct answer: 6 . 22549 V. Explanation: Let : C 1 = 3 . 81 μ F , C 2 = 6 . 9 μ F , C 3 = 13 . 1 μ F , and V = 17 . 5 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 = (17 . 5 V)(3 . 81 μ F) 3 . 81 μ F + 6 . 9 μ F = 6 . 22549 V . 002 (part 1 of 2) 10.0 points A coaxial cable with length ℓ 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 λ ≡ Q ℓ . ℓ radius = a + Q radius = b − Q b What is the electric field halfway between the conductors? 1. E = λ 2 π ǫ r 2 2. E = λ 4 π ǫ r 3. E = λ π ǫ r 4. E = Q π ǫ r 2 5. E = Q 4 π ǫ r 6. E = Q 2 π ǫ r 7. E = Q π ǫ r 8. E = Q 2 π ǫ r 2 9. E = λ π ǫ r 2 10. E = λ 2 π ǫ r correct Explanation: The electric field of a cylindrical capacitor is given by E = λ 2 π r ǫ . mcconnell (kam2342) – oldmidterm 02 – Turner – (60230) 2 003 (part 2 of 2) 10.0 points What is the capacitance C of this coaxial cable? 1. C = ℓ 2 k e ln parenleftbigg b a parenrightbigg correct 2. C = k e ℓ 2 ln parenleftbigg b a parenrightbigg 3. C = ℓ k e 4. C = ℓ 2 k e 5. C = ℓ k e ln parenleftBig a b parenrightBig 6. C = ℓ k e ln parenleftbigg b a parenrightbigg 7. C = 2 ℓ k e ln parenleftBig a b parenrightBig 8. C = ℓ a 2 k e b 9. C = k e ℓ ln parenleftbigg b a parenrightbigg 10. C = 2 ℓ k e ln parenleftbigg b a parenrightbigg Explanation: C = ℓ 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 8 . 6 μ F 62 . 8 μ F 47 . 9 μ F 8 4 . 3 μ F 91 . 2 V a b c d Find the capacitance between points a and b of the entire capacitor network. Correct answer: 130 . 074 μ F. Explanation: Let : C 1 = 18 . 6 μ F , C 2 = 47 . 9 μ F , C 3 = 62 . 8 μ F , C 4 = 84 . 3 μ F , and E = 91 . 2 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 mcconnell (kam2342) – oldmidterm 02 – Turner – (60230) 3 = (47 . 9 μ F) (62 . 8 μ F) 47 . 9 μ F + 62 . 8 μ F = 27 . 1736 μ F ....
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 Spring '10
 Turner
 Correct Answer, Electric charge, McConnell, μF

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