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Circuit Elements

Circuit Elements. Voltage and current sources Electrical resistance Kirchhoff’s Laws Resistive Circuits. Voltage and current sources. An electrical source is a device that is capable of converting nonelectric energy to electric energy (and vice versa)

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Circuit Elements

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  1. Circuit Elements • Voltage and current sources • Electrical resistance • Kirchhoff’s Laws • Resistive Circuits

  2. Voltage and current sources • An electricalsource is a device that is capable of converting nonelectric energy to electric energy (and vice versa) • An idealvoltagesource is a circuit element that maintains a prescribed voltage across its terminals regardless of current flowing in these terminals • An idealcurrentsource is a circuit element that maintains a prescribed current across its terminals regardless of voltage across the terminals

  3. Ideal voltage source Current-voltage characteristic Circuit symbol

  4. Ideal current source Current-voltage characteristic Circuit symbol

  5. Connections of ideal sources Valid connections

  6. Connections of ideal sources Invalid connections

  7. Connections of ideal sources Valid or invalid?

  8. Electrical resistance Resistance is the capacity of materials to impede the flow of current A resistor is a circuit element that displays this behavior Current-voltage characteristic Circuit symbol

  9. Electrical resistance, cont. Resistor’s obey Ohm’s Law: V = I R The voltage “drop” across a resistor is linearly proportional to the current passing through the resistor

  10. Electrical resistance, cont. Example #1 I = V/R = 5V/1E3W = 5mA

  11. Electrical resistance, cont. Example #2 What is voltage drop across R1 What is voltage polarity?

  12. Kirchhoff’s Laws A node is a point in a circuit where two or more elements meet

  13. Kirchhoff’s current law The algebraic sum of all the currents at any node in a curcuit equals zero I1 + I2 + I3 = 0

  14. Kirchhoff’s voltage law The algebraic sum of all the voltages around any closed path in a circuit equals zero VR3 + VR1 + VR2 + VC0 + VC4 = 0

  15. Resistors in series Using KVL and KCL, we have: -V1 + I*R1 + I*R2 = 0 or I*(10 + 20) = 30 ---- I = 30V/30W = 1A

  16. Resistors in series This is equivalent to: Resistors in series add together Rs = R1 + R2

  17. Resistors in parallel Using KVL and KCL, we have: I1 = 0.100A I2 = 0.033A V1 = I1R1 = I2R2 = 10V It = 0.100 + 0.033 = 0.133A

  18. Resistors in parallel This is equivalent to: Resistors in parallel are combined by adding their reciprocals 1/Rp = 1/R1 + 1/R2

  19. Classwork Find (a) the current through R3, (b) the current through R2, and (c) voltage across R1

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