# OHW 12 - terry(ect328 oldhomework 12 Turner(59130 This...

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terry (ect328) – oldhomework 12 – Turner – (59130) 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. 24 μ ± 57 33 73 94 V a b c d ±ind the capacitance between points a and b . Correct answer: 117 . 9 μ ±. Explanation: Let : C 1 = 24 μ ± , C 2 = 33 μ ± , C 3 = 57 μ ± , C 4 = 73 μ ± , and E = 94 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 = (33 μ ±) (57 μ ±) 33 μ ± + 57 μ ± = 20 . 9 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 = 24 μ ± + 73 μ ± + 20 . 9 μ ± = 117 . 9 μ ± . 002 (part 2 oF 2) 10.0 points What is the charge on the 33 μ ± upper- centered capacitor? Correct answer: 1964 . 6 μ C. Explanation: The voltages across C 2 and C 3 , respectively, (the voltage between a and b ) are V ab = V 23 = 94 V , and we have Q 23 = Q 3 = Q 2 = V ab C 23 = (94 V) (20 . 9 μ ±) = 1964 . 6 μ C . 003 (part 1 oF 2) 10.0 points Consider a air-flled parallel-plate capacitor with plates oF length 8 . 5 cm, width 6 . 61 cm, spaced a distance 1 . 01 cm apart. Now imagine that a dielectric slab with di- electric constant 5 . 6 is inserted a length 4 . 8 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 . 8 cm.

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terry (ect328) – oldhomework 12 – Turner – (59130) 2 A battery is connected to the plates so that they are at a constant potential 0 . 66 V while the dielectric is inserted. 8 . 5 cm 4 . 8 cm 1 . 01 cm dielectric none - air bottom 1 . 0 dielectric constant top 5 . 6 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: 3
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OHW 12 - terry(ect328 oldhomework 12 Turner(59130 This...

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