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ps04

# ps04 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of...

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PS04-1 MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Physics 8.02 Fall 2008 Label with your name, table number and group. Turn in at the homework box. Problem Set 4 Due: Thursday, October 2 nd at 12:00 pm Warm Up Problem 1: Parallel Plate Capacitor A parallel-plate capacitor is charged to a potential V 0 and charge Q 0. It is then disconnected from the battery. The separation of the plates is then halved. What happens to: (a) the charge on the plates? (b) the electric field? (c) the energy stored in the electric field? (d) the potential? (e) How much work did you do in halving the distance between the plates? Exam Problem Problem 2: Capacitor A parallel plate capacitor has capacitance C . It is connected to a battery of voltage V until fully charged, and then disconnected. The plates are then pulled apart an extra distance d , during which the measured potential difference between them changed by a factor of 2. Below are a series of questions about how other quantities changed. Although they are related you do not need to rely on the answers to early questions in order to correctly answer the later ones. a) Did the potential difference increase or decrease by a factor of 2? b) By what factor did the electric field change due to this increase in distance? Make sure that you indicate whether the field increased or decreased. c) By what factor did the energy stored in the electric field change? Make sure that you indicate whether the energy increased or decreased. d) A dielectric of dielectric constant κ is now inserted to completely fill the volume between the plates. Now by what factor does the energy stored in the electric field change? Does it increase or decrease?

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