p240_ct9_f07

# p240_ct9_f07 - Physics 240 Fall 2007 Lecture #9 First exam...

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Physics 240 Fall 2007 Lecture #9 Dr. Dave Winn 2405 Randall Lab winn@umich.edu First exam Thursday night, October 4, 8:00-9:30

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Information on Exam #1 First exam Thursday night, Oct. 4, from 8:00- 9:30 Covers chapters 21-24.2 (only a few capacitor problems) You will be asked to present your ID when you turn in the exam Exam will include 20 multiple choice questions based on MP, discussion, and in class work. Bring calculator, 3”x5” note card (both sides), and #2 pencil Practice exams are available online.
Introduction to capacitors As we begin to explore the use of electricity, we need tools. One basic tool is a storage device; the “capacitor” Capacitors store charge and energy “Capacitance” is a measure of the economy with which an object stores charge

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The basic idea Generally, capacitors separate positive and negative charge on two separate parts Capacitance is a measure of how much charge can be stored on these objects at a given potential difference C = Q/V C = charge stored / work to store it each unit charge +Q -Q E
The basic idea C = Q/V To increase C, you generally make the object large (more Q can be stored) and move the parts closer together (less potential difference between them) +Q -Q E

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The archetype: parallel plates Two charge plates, area A (~L 2 ), charge +Q and –Q, separation d If d << L then we know: E = σ / ε 0 =(Q/A ε 0 ) Δ V +- = Ed Call this potential change V V = (Q/A ε 0 )d Q = (A ε 0 /d)V ++++++++++++++++++++++++++++++ --------------------------------------------------- L d
The archetype: parallel plates Q = (A ε 0 /d)V First part depends only

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## This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Fall '08 term at University of Michigan.

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p240_ct9_f07 - Physics 240 Fall 2007 Lecture #9 First exam...

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