hw 18 - nguyen (jmn727) – homework 18 – Turner –...

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Unformatted text preview: 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 , 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.

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hw 18 - nguyen (jmn727) – homework 18 – Turner –...

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