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Unformatted text preview: nguyen (jmn727) – homework 18 – Turner – (59070) 1 This printout should have 9 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An airfilled 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 , ℓ = 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 = ℓ 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 = constant so that E ′ = 2 Q 2 A ǫ 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....
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This note was uploaded on 01/21/2010 for the course PHY 303L taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
 Turner
 Capacitance, Work

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