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Chapter 6 Series-Parallel Circuits EGR 101 1 Examples of Series-Parallel Circuits EGR 101 2 Basic Configurations EGR 101 3 An Example for Analysis: Series Circuits Connected in Parallel EGR 101 4 Team Activity: Problem 1 on p. 173 – Method 1 • Use the voltage divider method to calculate the voltages across R1 & R2. • Use the voltage divider method to calculate the voltages across R3 & R4. • Calculate the current through R1 & R2. • Calculate the current through R3 & R4. • Calculate the total current IT. EGR 101 5 Team Activity: Problem 1 on p. 173 – Method 2 • Find the equivalent resistances R12 & R34. • Find the total resistance RT. • Find the total current IT. EGR 101 6 A Second Example: Parallel Circuits Connected in Series EGR 101 7 Team Activity: Problem 5 on p. 174. • Find the equivalent resistances R12 & R34. • Calculate the total current IT. EGR 101 8 Wheatstone Bridge Galvanometer – a sensitive ammeter EGR 101 9 • Bridge Operation – based on three possible states: VA = VB VA > VB VA < VB EGR 101 10 Wheatstone Bridge: A series-parallel arrangement at “balance” • Resistors R1 and R2 are in series – R12 = R1 + R2 • Resistors R3 and R4 are in series – R34 = R3 + R4 • Equivalent resistance R12 is in parallel with equivalent resistance R34 EGR 101 11 Circuit Analysis at “balance”, galvanometer current =0 R V V R R R V V R R V V 2 A S 1 2 4 B S 3 A 4 B R R R R R R R R R R 2 1 EGR 101 4 2 3 2 4 1 3 4 12 Application of a Wheatstone Bridge: Smoke Detector Photoconductive Cells – Light-Controlled Resistors Used as Sensor and Reference When the amount of light striking the device increases, the resistance decreases (and vice-versa). EGR 101 13 Detector Diagram EGR 101 14 How it works When the air is clear, the bridge is balanced. If smoke enters the lower chamber via the vents, the resistance of the lower photoconductive cell increases, causing the bridge to become unbalanced, triggering the alarm. SMOKE EGR 101 15