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DC circuits

1. Battery Model 2. Simple series and parallel 3. Combo series and parallel 4. RC circuits 5. Kirchhoff’s Laws www.rideau-info.com . DC circuits. Animation - DC Circuits. Pressure drops (voltage drops) all add Flow rate in = flow rate out (current in = current out).

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DC circuits

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  1. 1. Battery Model2. Simple series and parallel3. Combo series and parallel4. RC circuits5. Kirchhoff’s Lawswww.rideau-info.com DC circuits

  2. Animation - DC Circuits • Pressure drops (voltage drops) all add • Flow rate in = flow rate out (current in = current out) http://faraday.physics.utoronto.ca/IYearLab/Intros/DCI/Flash/WaterAnalogy.swf

  3. Battery Model • Voltage source and internal resistance • Source electrochemical “emf” • Internal resistance • Resistance increases with time (battery goes bad) • Model is series of voltage and resistance

  4. Example 19-1 (1) • Find current (voltages add to 0) • Find voltage drops

  5. Example 19-1 (2) • Find voltage across battery • Find Power consumed by resistors • Find Power delivered by battery

  6. Simple Series Circuit • Rules for Series • Voltages add • Current same • Equivalent circuit • Equivalent series resistance • Example (12 v battery, 4 Ω resistors)

  7. Simple Parallel Circuit • Rules for Parallel • Voltage same • Currents add • Equivalent circuit • Equivalent parallel resistance • Example (12 v battery, 4 Ω resistors)

  8. Series vs. Parallel • Criterion for series and parallel (do not confuse!) • Weird geometries

  9. Simple Series and Parallel • Example 19-3 Parallel, R = 100 Ω • Find I through each resistor (V same) • Find total current I = I1 + I2 , • Find apparent R = V/I • Example 19-3 Series R = 100 Ω • Add V across both resistors (I same) • Find common current • Find apparent R = V/I

  10. Combo Series and Parallel - 19.4 • Progressively simplify • Find equivalent resistances • Parallel, series, series • Total resistance 690 Ω • Find current through battery • Reconstruct voltage drops currents • Current through 400 Ω (same as battery) • Voltage across 400 Ω • Voltage across 500/700 • Currents through 500/700 • etc, etc.

  11. Combo Series and Parallel 19.5 • Build it back up • Find voltage drop near battery • Find other voltage drops • Find currents, etc, and continue • Current through battery 17 mA • Current through 400 Ω also 17 mA • Voltage across 400 Ω • Voltage across 500/700 12 V – 6.8 V = 5.2 V • Currents through 500/700 I1=10 mA I2=7 mA

  12. Combo Series and Parallel 19.7 • Simplify down • Rtot = 10.3 Ω • Ibat = 0.87 A • Build back up • Voltage across top • Current through 10 Ω • Current through 8.7 Ω • Current through 6 Ω • Voltage across 4/8 Ω

  13. More complicated series parallel • Example 19-7 • Current from battery • Drop across battery • Current in 6Ω resistor • Solution • Get total resistance (break down) • Get total I • Establish IR drops (build up) • Find current • Like solving crossword puzzle!

  14. Car Talk Puzzler* Go out to start your car. New battery, radio works, but electrical goes dead when you try to start. • Starter Motor • Estimate power (1600 W) • Estimate current (133 A) • Estimate resistance (.09 ohms) • Radio • Estimate power (100 W) • Estimate current (8 A) • Estimate resistance (1.5 ohms) • Draw circuit, parallel starter/radio in series with battery and cable/contact resistance. (0.1 ohms) *Apologies to Click & Clack

  15. Example - Problem 20

  16. More examples • Chapter 19 - 13, 14, 17, 19, 20 - Resistors in series and parallel

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