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Jan28Note - PHYS142 Lecture 10 Capacitance and Dielectrics Chapter 26 All sections except 6 26.1 26.2 26.3 26.4 26.5 26.7 Definition of Capacitance

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Capacitance and Dielectrics • Chapter 26 All sections except 6 26.1 Definition of Capacitance 26.2 Calculating Capacitance 26.3 Combinations of Capacitors 26.4 Energy Stored in a Charged Capacitor 26.5 Capacitors with Dielectrics 26.7 An Atomic Description of Dielectrics PHYS142 Lecture 10 2
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Definition of Capacitor (26.1) A pair of conducting objects (surfaces) separated by a gap constitute a capacitor . If a capacitor is connected to a battery , after a very short time each plate acquires a charge. + + + + + + _ _ _ _ _ _ V + Q - Q + 6
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The amount of charge is directly proportional to the potential difference of the battery. Q ~ V The charge on the capacitor is defined to be the charge on its positively charged plate . Q = CV Where C is the capacitance of the capacitor. Capacitance refers to the “capacity to accumulate charges” If C is large, so is Q for a given V . Units for Capacitance: C/V Farad [F] Definition of capacitance 7
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True or False? From the definition of capacitance C = Q/ΔV, it follows that an uncharged capacitor has a capacitance of zero . 1 2 72% 28% 1. True 2. False Question 1
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True or False? (a) As described by the definition of capacitance C = Q/ΔV, it follows that the potential difference across an uncharged capacitor is zero. 1 2 23% 77% 1. True 2. False Question 2
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The capacitance C depends on the construction of the capacitor i.e. its geometry and the material in the gap.
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This note was uploaded on 02/22/2011 for the course PHYS 142 taught by Professor Altounian during the Spring '07 term at McGill.

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Jan28Note - PHYS142 Lecture 10 Capacitance and Dielectrics Chapter 26 All sections except 6 26.1 26.2 26.3 26.4 26.5 26.7 Definition of Capacitance

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