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Introduction To Engineering Electrical Circuits - 2. Agenda Kirchhoff’s Law Resistors & Resistance Wheatstone Bridge. Kirchhoff’s Laws. Voltage Law: The sum of the voltage rises around a closed loop in a circuit must equal the sum of the voltage drops.
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Introduction To EngineeringElectrical Circuits - 2 Agenda Kirchhoff’s Law Resistors & Resistance Wheatstone Bridge
Kirchhoff’s Laws • Voltage Law:The sum of the voltage rises around a closed loop in a circuit must equal the sum of the voltage drops. • Current Law:The sum of all currents into a junction (node) must equal the sum of all currents flowing away from the junction.
Resistors in Series Applying Kirchhoff’s voltage law gives us: V = I R1 + I R2 + I R3
Resistors in Parallel voltage law: V = I1R1 = I2R2 = I3R3 current law: Ix = I1 + Iy and Iy = I2 + I3
R1 Req R2 R3 Equivalent Resistance If desired, several resistors can sometimes be replaced by a single “equivalent” resistor: Req = R1 + R2 + R3 + … For resistors in series:
Req R1 R2 R3 Equivalent Resistors (cont) For Resistors in Parallel
R1 R2 R3 Student Problem: • If each of the R’s were 60 W light bulbs, (R =240 ohm), what would be the equivalent resistance for all three bulbs in parallel. • What would be the total power draw for the three bulbs V = I x R P = V x I
Wheatstone Bridge Circuit with resistors in both series and parallel configurations. Used in strain gages, alarm circuits, and many other systems. The bridge is “balanced” when im = 0, at which point: R1/R2 = R3/R4
Assignment #29 • Do problem set 2 on electrical circuit drawings found in the assignment packet.