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Lecture 2

Lecture 2. 2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws. Voltage and Current Sources. Independent Sources. Characteristics. An independent source establishes a voltage or current in a circuit without relying on voltages and currents elsewhere in the circuit.

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Lecture 2

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  1. Lecture 2 2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws

  2. Voltage and Current Sources

  3. Independent Sources

  4. Characteristics • An independent source establishes a voltage or current in a circuit without relying on voltages and currents elsewhere in the circuit. • The value of the voltage or current supplied is specified by the value of the independent source alone.

  5. Exercise

  6. Dependent Sources

  7. Characteristics • Dependent sources establish a voltage or current whose value depends on the value of a voltage or current else where in the circuit. • You cannot specify the value of a dependent source unless you know the value of the voltage or current on which it depends.

  8. Exercise

  9. Exercise What value of Vg is required for the wiring to be valid?

  10. Ohm’s Law

  11. Analogy • The height of the water=voltage • The volume of flow through the hole • per second=current • The smallness of the hole = resistance • Water wheel hit by the flow from the hole = power

  12. Thought Experiment #1 Fixed hole dimension↔ Fixed R Height of water↑ → flow rate↑. V↑ → I↑

  13. Thought Experiment #2 Fixed height of water↔ Fixed V Hole dimension↑ → flow rate↑ R↓ → I↑

  14. Derivation of Ohm’s Law • Three variables: V,I and R. • Different Possibilities: • V=IR (1) • I=VR (2) • R=VI (3) • Intuition • If R is constant, V↑ → I↑. • (3) is not possible. (1) and (2) are possible. • If V is constant, R↓ → I↑. • (2) and (3) are not possible

  15. Ohm’s Law • V=IR • Mnemonic: Victory Is Rare

  16. Exercise • Calculate the value va • Determine the power dissipated in the resistor

  17. Exercise Calculate id

  18. Kirchhoff’s Laws

  19. KCL • Kirchhoff’s Current law (KCL) • The algebraic sum of all the currents at any node in a circuit equals zero

  20. Exercise Sum the currents at each node

  21. Multisim Demo

  22. KVL • Kirchhoff’s Voltage Law • The algebraic sum of all the voltage around any closed path in a circuit equals zero

  23. Exercise Sum the voltages around each designated path in the circuit

  24. Example 2.8 KCL at b KVL around cabc loop Solve for io and i1

  25. Problem 2.18 KCL at the top node KVL around the right loop Find i1, i2, vo

  26. Problem 2.21 Find i1 if i0 is 1A.

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