oldhw 12 - nguyen (jmn727) oldhomework 12 Turner (59070)...

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nguyen (jmn727) – oldhomework 12 – Turner – (59070) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 (part 1 oF 2) 10.0 points ±our capacitors are connected as shown in the fgure. 17 μ ± 59 46 84 97 V a b c d ±ind the capacitance between points a and b . Correct answer: 126 . 848 μ ±. Explanation: Let : C 1 = 17 μ ± , C 2 = 46 μ ± , C 3 = 59 μ ± , C 4 = 84 μ ± , and E = 97 V . C 1 C 3 C 2 C 4 E B 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 defnition 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 = (46 μ ±) (59 μ ±) 46 μ ± + 59 μ ± = 25 . 8476 μ ± . The total capacitance C ab between a and b can be obtained by calculating the capacitance in the parallel combination oF the capacitors C 1 , C 4 , and C 23 ; i.e. , C ab = C 1 + C 4 + C 23 = 17 μ ± + 84 μ ± + 25 . 8476 μ ± = 126 . 848 μ ± . 002 (part 2 oF 2) 10.0 points What is the charge on the 46 μ ± upper- centered capacitor? Correct answer: 2507 . 22 μ C. Explanation: The voltages across C 2 and C 3 , respectively, (the voltage between a and b ) are V ab = V 23 = 97 V , and we have Q 23 = Q 3 = Q 2 = V ab C 23 = (97 V) (25 . 8476 μ ±) = 2507 . 22 μ C . 003 (part 1 oF 2) 10.0 points Consider a air-flled parallel-plate capacitor with plates oF length 9 . 4 cm, width 6 . 19 cm, spaced a distance 1 . 15 cm apart. Now imagine that a dielectric slab with di- electric constant 3 . 4 is inserted a length 4 . 2 cm into the capacitor. The slab has the same width as the plates. The capacitor is com- pletely flled with dielectric material down to a length oF 4 . 2 cm.
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nguyen (jmn727) – oldhomework 12 – Turner – (59070) 2 A battery is connected to the plates so that they are at a constant potential 0 . 17 V while the dielectric is inserted. 9 . 4 cm 4 . 2 cm 1 . 15 cm dielectric none - air bottom 1 . 0 dielectric constant top 3 . 4 What is the ratio of the new potential en- ergy to the potential energy before the inser- tion of the dielectric? Edge eFects can be neglected. Correct answer: 2
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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.

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oldhw 12 - nguyen (jmn727) oldhomework 12 Turner (59070)...

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