p240_ct13_f07 - Physics 240 Fall 2007 Lecture #13 Dr. Dave...

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Unformatted text preview: Physics 240 Fall 2007 Lecture #13 Dr. Dave Winn 2405 Randall Lab [email protected] Kirchoff’s rules for circuits Two basic rules: 1. The sum of potential changes around any loop in a circuit must be zero (Loop Rule) 2. The sum of currents entering any junction must equal the sum of currents leaving it. (Junction Rule) +- A B V V – IR A – IR B = 0 +- A V B I in I A I B I in = I A + I B Equivalent resistance: series Current through R 1 equals current through R 2 V Bat = V 1 + V 2 = IR 1 + IR 2 V Bat = V eq = IR eq IR eq = IR 1 + IR 2 R eq = R 1 + R 2 R 2 R 1 R eq + _ + _ V Bat V 2 = IR 2 V 1 = IR 1 V Bat R = ρ (L/A) Bigger L! Loop rule! Equivalent resistance: parallel V = I 1 R 1 = I 2 R 2 I 1 = V / R 1 I 2 = V / R 2 I = I 1 + I 2 V = IR eq or I = V / R eq V / R eq = V / R 1 + V / R 2 1/R eq = 1/R 1 + 1/R 2 R = ρ (L/A) Bigger A! Junction rule! Loop rule! +- V R 1 R 2 +- V R eq I I 1 I 2 The circuit in front of you contains a single lightbulb, bulb A, that burns with a certain brightness. We will now add an identical bulb, bulb B, in series with bulb A. What will happen? 1) Both will shine with the same brightness as bulb A did before. 2) Both will shine with equal brightness, but they will be dimmer than before. 3) Both will shine with equal brightness, but they will be brighter than before. 4) Bulb A will be brighter than bulb B. 5) Bulb B will be brighter than bulb A. 6) Whether A or B is brighter depends on the direction of the current. I bulb =V bulb /R total R total = 2R bulb I is reduced The circuit in front of you contains a single lightbulb, bulb A, that burns with a certain brightness. We will now add an identical bulb, bulb B, in parallel with bulb A. What will happen?...
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This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Fall '08 term at University of Michigan.

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p240_ct13_f07 - Physics 240 Fall 2007 Lecture #13 Dr. Dave...

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