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. 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 v a Determine the power dissipated in the resistor

17. Exercise Calculate i d

18. Kirchhoff’s Laws

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

21. Exercise Sum the currents at each node

22. Multisim Demo

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

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

25. Example 2.8 1.KCL at b 2.KVL around cabc loop 3.Solve for i o and i 1

26. Problem 2.18 1.KCL at the top node 2.KVL around the right loop 3.Find i 1, i 2, v o

27. Problem 2.21 Find i 1 if i 0 is 1A.