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Unformatted text preview: Platt, David Homework 8 Due: Sep 26 2005, 4:00 am Inst: Ken Shih 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. The due time is Central time. For 003 you need give your answer in unit of pF (1pF=e-12*F). 001 (part 1 of 2) 10 points Consider a air-filled parallel-plate capacitor with plates of length 8 . 8 cm, width 6 . 78 cm, spaced a distance 1 . 86 cm apart. Now imagine that a dielectric slab with di- electric constant 2 . 7 is inserted a length 4 . 8 cm into the capacitor. The slab has the same width as the plates. The capacitor is com- pletely filled with dielectric material down to a length of 4 . 8 cm. A battery is connected to the plates so that they are at a constant potential 0 . 83 V while the dielectric is inserted. 8 . 8 cm 4 . 8 cm 1 . 86 cm dielectric none - air bottom 1 . dielectric constant top 2 . 7 What is the ratio of the new potential en- ergy to the potential energy before the inser- tion of the dielectric? Edge effects can be neglected....
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