Unformatted text preview: t be zero. WHY?
The potential difference between a point and itself is zero ! Physics 212 Lecture 10, Slide 6 Kirchoff’s Current Rule ∑I in = ∑ I out Kirchoff's Current Rule states that the sum of all
currents entering any given point in a circuit must equal
the sum of all currents leaving the same point. WHY?
Electric Charge is Conserved
Electric Physics 212 Lecture 10, Slide 7 Kirchhoff’s Laws
(1) Label all currents
Choose any direction (2) Label +/- for all elements R1 A + I1 + Current goes + ⇒ - (for resistors) (3) Choose loop and direction
Must start on wire, not element. 3 + B
1 - First sign you hit is sign to use. I2 I3 - +
2 (4) Write down voltage drops + R2 R3 R5 - + I4 - R4 + + I5 (5) Write down node equation
Iin = Iout We’ll do calculation first today
It’s actually the easiest thing to do !! Physics 212 Lecture 10, Slide 8
17 Preflight 3
DROP GAIN BB N
20 With the current
Against the current VOLTAGE DROP
VOLTAGE GAIN 10
0 Physics 212 Lecture 10, Slide 9 1Ω
1Ω Calculation 2V 1V I2 In this circuit, assume Vi and Ri are known.
What is I2 ?? 1V • Conceptual Analysis:
– Circuit behavior described by Kirchhoff’s Rules:
• KVR: ΣVdrops = 0
• KCR: ΣIin = ΣIout •Strategic Analysis
– Write down Loop Equations (KVR)
Write down Node Equations (KCR)
Solve Physics 212 Lecture 10, Slide 10
10 V1 R1
++ - -+ + R3
- - V2 R2 I2 In this circuit, assume Vi and Ri are known. -...
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- Spring '11
- Physics, SEPTA Regional Rail, Ri, Voltage drop, University City, Jenkintown-Wyncote