capacitors 1

capacitors 1 - Last Week Petrus van Musschenbroek 1692-1761...

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1 1 Capacitors – I Petrus van Musschenbroek 1692-1761 Made first capacitor. Also Ewald von Kleist 1715-1759 This lecture: HRW 25.1-25.3 For next time: HRW 25.4-25.8 Exam-related problem session, next Monday, here at 4:40-6:20. 2 Last Week Electric Potential: U=V Q Potential and Work: W = Q(V B -V A ) is the work W required to move a charge Q from A to B In 1D, Conductors are equipotentials; charge tends to accumulate on surfaces with greater curvature. Today Capacitors and Capacitance Calculating capacitance: Parallel plate capacitor Spherical capacitor x dV E= - dx 3 A capacitor is two isolated conductors (called plates ) of any shape. With Δ V between the plates, one collects a charge Q, and the other –Q. For capacitors, Δ V is called V. Units of capacitance: Farad (F) = Coulomb/Volt Capacitors and Capacitance -Q +Q Don’t confuse capacitance, C, with units of charge (Coulombs) V is proportional to Q, and the proportionality constant is called the capacitance, C. Capacitance depends only on: geometry -- the shape, separation and orientation of the conductors. materials -- the substance between the conductors. Q C= V 4 Electrolytic (1940-70) Electrolytic (new) Paper (1940-70) Tantalum (1980 on) Ceramic (1930 on) Mica (1930-50) Variable air, mica
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2 5 Charging a Capacitor A battery or electric power supply maintains a fixed V across its terminals, (by internally moving electrons). 1.5V -Q +Q Electrons flow from the battery until the voltage across the capacitor is V o .
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This note was uploaded on 04/05/2008 for the course PHYS 212L taught by Professor Huang,tai-yin during the Spring '07 term at Penn State.

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capacitors 1 - Last Week Petrus van Musschenbroek 1692-1761...

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