2. Electric Circuits (EELE 2312) Chapter 1 Circuit Variables & Circuit Elements Basil Hamed

3. Circuit Theory Mathematical model that approximates the behavior of an actual electrical system Commonly used to refer to an actual electrical system as well as to the model that represents it Basil Hamed2

4. Problem Solving Identify what ’ s given and what ’ s to be found Sketch a circuit diagram or other visual model Think of several solution methods and choose one Calculate a solution Use your creativity Test your solution Basil Hamed3

5. 4 The SI Units QuantityBasic UnitSymbol Lengthmeterm MasskilogramKg TimesecondS Electric CurrentampereA Temperaturedegree kelvin oKoK Luminous intensitycandelacd

6. 5 1.1 Circuit Analysis An Overview Need Design Specifications Concept Circuit Model Ideal Circuit Components Circuit Analysis Physical Prototype Need Design Specifications Concept Circuit Model Ideal Circuit Components Circuit Analysis Physical Prototype

7. 6 The Charge is bipolar (+ve & -ve) Electric Charge exists in discrete quantities (1.6022×10 -19 C) Electrical Effects attributed to separation of charges and charges in motion Separation of charges expends energy. Voltage is the energy per unit charge created by the separation of charges. The electrical effects caused by charges in motion depend on the rate of charge flow. Electric Current is the rate of charge flow. 1.2 Voltage, Current, & The Basic Circuit Element The concept of Electric Charge is the basis for understanding all electrical phenomena

8. 7 1.3 The Ideal Basic Circuit Element Two terminals connected to other circuit components It is described mathematically in terms of current and/or Voltage It can not be subdivided

9. 8 Passive Sign Convention Whenever the reference direction for the current in an element is in the direction of the reference voltage drop across the element use a positive sign in any expression that relates the voltage to the current. Otherwise, use a negative sign.

10. 9 1.4 Power and Energy Power: time rate of expending or absorbing energy

11. 10 1.4 Power and Energy Working Example i=4 A and ʋ =-10 V P=-(-10)(4)=40 W

12. 11 An Ideal Current Source is a circuit element that maintains a prescribed current through its terminals regardless of the voltage across those terminals An Ideal Voltage Source is a circuit element that maintains a prescribed voltage across its terminals regardless of the current flowing in those terminals Electrical Source is a device that is capable of converting nonelectric energy to electric energy and vice versa 1.5 Voltage and Current Sources

13. 12 An Independent Source establishes a voltage or current in a circuit without relying on voltages or currents elsewhere in the circuit 1.5 Voltage and Current Sources Independent Sources

14. 13 A dependent Source (Controlled Source) establishes a voltage or current whose value depends on the value of a voltage or a current elsewhere in the circuit 1.5 Voltage and Current Sources Dependent Sources μ, ρ, α, and β are multiplying constants Active Elements capable of generating electric energy Passive Elements cannot generate electric energy

15. 1.5 Voltage and Current Sources There are five ideal basic circuit elements: voltage sources, current sources, resistors, inductors, and capacitors 14

16. 1.5 Voltage and Current Sources Active element is one that models a device capable of generating electric energy. Voltage sources and Current sources are example active circuit elements. Passive elements model physical devices that cannot generate electric energy. Resistors, inductors, and capacitors are examples of passive circuit elements. 15

17. 16 Using the definition of the ideal independent voltage and current sources, state which interconnections in the following figures are permissible and which violate the constraints imposed by the ideal sources Example 1.1 Valid Invalid Valid

18. 17 Using the definition of the ideal independent and dependent sources, state which interconnections in the following figures are valid and which violate the constraints imposed by the ideal sources Example 1.2 Invalid Valid Invalid

19. Electrical Resistance Resistance is the capacity of materials to impede the flow of current or, more specifically, the flow of electric charge. The circuit element used to model this behavior is the resistor. 18

20. 19 Electrical Resistance Ohm’s Law

21. 20 In each of the following circuits υ or i is not known. (a) Calculate the value of υ or i, (b) Determine the power dissipated in each resistor. Example 1.3 8 V 10 A -20 V -2 A

22. Example 1.3 b) The power dissipated in each of the four resistors is 21

23. 22 Kirchhoff’s Laws Kirchhoff’s Current Law 7 Unknowns The algebraic sum of all currents at any node in a circuit equals zero

24. 23 Kirchhoff’s Laws Kirchhoff’s Voltage Law The algebraic sum of all voltages around any closed path in a circuit equals zero

25. 24 Example 1.4 Sum the currents at each node in the circuit shown. Note that there is no connection dot (●) in the center of the diagram.

26. 25 Example 1.5 Sum the voltages around each designated path in the circuit shown.

27. 26 Use Kirchhoff ’ s laws and Ohm ’ s law to find i o in the circuit shown and test the solution for i o by verifying that the total power generated equals the total power dissipated. Example 1.6

28. 27 The terminal voltage and the terminal current were measured on the device shown in the figure shown and the values are tabulated. (a) construct a circuit model of the device inside the box, (b) using the circuit model, predict the power this device will deliver to a 10 Ω resistor. Example 1.7

29. 28 Analysis of Circuits Containing Dependent Sources

30. 29 Example 1.8 Use Kirchhoff ’ s laws and Ohm ’ s law to find the voltage υ o in the circuit shown and test the solution by verifying that the total power developed equals the total power dissipated.

31. Basil Hamed30 End of Chapter One