Lecture 25a

# Lecture 25a - Chapter 25: Capacitors Capacitor: A pair of...

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Chapter 25: Capacitors

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For a “charged” capacitor, one conductor is + the other is – (net charge is zero) The work used in separating charge is stored as electrostatic potential energy in the capacitor. C apacitor: A pair of conductors, insulated from each other, used to store energy
Definition of Capacitance C q C V +q -q V Charge q is proportional to potential difference V between the plates Units: farad [F]

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Parallel-Plate capacitor What is the capacitance of a parallel plate capacitor of area A and separation d ? (Work out on board) 0 A C d Depends on geometry! Fringe field outside
5 L L d A parallel-plate capacitor has square plates of edge length L, separated by a distance d. If we doubled the dimension L and halve the dimension d, by what factor have we changed the capacitance? A)1.0 B) 2.0 C) 4.0 D) 16.0 E) None of the above. 0 A C d

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6 How big is a one Farad Capacitor? Assume you have two parallel plates that are separated by 1 mm. If you estimate 0 ~ 10 -11 , what is the area of the plates to have a 1.0 Farad capacitance? A)100,000,000 square meters B) 1,000 square meters C) 1 square meter D) 0.1 square meters E) 0.001 square meters 0 A C d
7

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## This note was uploaded on 02/05/2011 for the course PHYS 220B taught by Professor Preminger during the Fall '10 term at CSU Northridge.

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Lecture 25a - Chapter 25: Capacitors Capacitor: A pair of...

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