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# hw 18 - nguyen(jmn727 homework 18 Turner(59070 This...

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nguyen (jmn727) – homework 18 – Turner – (59070) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An air-filled cylindrical capacitor has a capac- itance of 15 pF and is 2 . 8 cm in length. The coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 . If the radius of the outside conductor is 1 . 5 cm, what is the required radius of the inner conductor? Correct answer: 1 . 35204 cm. Explanation: Let : k e = 8 . 98755 × 10 9 N · m 2 / C 2 , = 2 . 8 cm = 0 . 028 m , b = 1 . 5 cm , and C = 15 pF = 1 . 5 × 10 11 F . The capacitance of a cylindrical capacitor is given by C = 2 k e ln b a where a and b are the inner and outer radii, respectively. Solving for a , we obtain a = b e ℓ/ (2 k e C ) = (1 . 5 cm) e (0 . 028 m) / [2 k e (1 . 5 × 10 - 11 F)] = 1 . 35204 cm . 002 10.0 points If the plate separation of an isolated parallel plate capacitor is doubled, 1. the charge density on each plate is dou- bled. 2. the charge on the each plate is halved. 3. the electric field is doubled. 4. None of these correct 5. the potential difference is halved. Explanation: Q and A are constant, so E = Q A ǫ 0 = constant so that E = 2 Q 2 A ǫ 0 and V = Q C = 2 Q C = 2 Q C = 2 V . 003 (part 1 of 2) 10.0 points Consider the system of capacitors connected to a battery as shown below. E B 3 μ F 3 μ F 3 μ F 3 μ F 3 μ F 3 μ F Find the equivalent capacitance of the cir- cuit. 1. C = 4 μ F 2. C = 3 μ F 3. C = 3 2 μ F 4. C = 2 μ F correct 5. C = 4 3 μ F 6. C = 2 3 μ F 7. C = 1 μ F Explanation:

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nguyen (jmn727) – homework 18 – Turner – (59070) 2 E B C 1 C 2 C 3 C 4 C 5 C 6 c a b c d Let : C 1 = C = 3 μ F , C 2 = C = 3 μ F , C 3 = C = 3 μ F , C 4 = C = 3 μ
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