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Unformatted text preview: Physics 212 Fall 2009 Circuits  9/23/09 Current and Resistance a b V=V bV a i Ohmic Devices: P = IV V = IR P = I ( IV ) = I 2 R = V R 2 R = V 2 R i = Δ q Δ t (A)mpere=(C)oulomb/(s)econd v d = i A 1 ne Current R ≡ V i Ohm=Volt/Amp R = ρ L A Resistance A ⋅ V = C s J C = J s = ( W ) att Δ U Δ t = P = iV Power Electromotive Force (EMF) EMF  Ability to do work on charges EMF Sources battery generators solar cells thermopiles fuel cells human body Many different ways to power a circuit E is not V Internal Resistance  possibly due to corrosion reduces available EMF 12 V battery does not always deliver 12 V Available EMF is reduced when you start your car due to large current draw through the battery Notice your headlights will dim briefy Power headlights Available EMF ε = V − ir = 12 − 0.1 V = 11.9 V V = ir = (10 A )(0.01 Ω ) = 0.1 V Start your car Available EMF ε = V − ir = 12 − 1.0 V = 11.0 V V = ir = (100 A )(0.01 Ω ) = 1.0 V Solving Circuits Potential Method  Rules  Kirchhoff’s Junction Rule sum of currents into a junction equals the sums of the currents out of a junction...
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This note was uploaded on 10/03/2011 for the course PHYS 212 taught by Professor Tedeschi during the Fall '08 term at South Carolina.
 Fall '08
 TEDESCHI
 Current, Resistance, Power

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