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13 - Circuits

13 - Circuits - Physics 212 Fall 2009 Circuits Current and...

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Physics 212 Fall 2009 Circuits - 9/23/09

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Current and Resistance a b V=V b -V 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

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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 briefly 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 Kirchhoff’s Loop Rule

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13 - Circuits - Physics 212 Fall 2009 Circuits Current and...

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