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Unformatted text preview: Kirchhoff’s Laws Physics 102: Lecture 06 Note opposite sign convention compared to your handouts! Last Time ... 3 2 1 + + + = R R R R eq • Resistors in series: • Resistors in parallel: ... 1 1 1 1 3 2 1 + + + = R R R R eq Current thru is same; Voltage drop across is IR i Voltage drop across is same; Current thru is V/R i Last Lecture • Solved Circuits • What about this one? Today 5 Kirchhoff’s Rules • Kirchhoff’s Junction Rule (KJR): – Current going in equals current coming out. • Kirchhoff’s Loop Rule (KLR): – Sum of voltage drops around a loop is zero. 12 Using Kirchhoff’s Rules (1) Label all currents Choose any direction (2) Label +/ for all elements Current goes + ⇒ (for resistors) (3) Choose loop and direction (4) Write down voltage drops Be careful about signs R 4 + + + + + + + + R 1 ε 1 R 2 R 3 ε 2 ε 3 R 5 A B 17 I 1 I 3 I 2 I 4 I 5 Loop Rule Practice R 1 =5 Ω I ε 1 = 50V R 2 =15 Ω ε 2 = 10V A B Find I: 22 Loop Rule Practice R 1 =5 Ω I + ε 1  IR 1 ε 2 IR 2 = 0 +50  5 I  10  15 I = 0 I = +2 Amps ε 1 = 50V + + + + R 2 =15 Ω ε 2 = 10V A B Find I: 22 Label currents Label elements +/ Choose loop Write KLR Opposite sign convention compared to your handouts! ACT: KLR...
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This note was uploaded on 01/25/2012 for the course PHYS 102 taught by Professor Lee during the Spring '08 term at University of Illinois, Urbana Champaign.
 Spring '08
 Lee
 Physics, Current

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