1. Introduction; Units (1. 1); Basic Quantities (1
Introduction; Units (1.1); Basic Quantities (1.2); Circuit Elements (1.3)
Dr. Holbert
January 18, 2006
ECE201 Lect-1

2. Basic Electrical Quantities
Basic quantities: current, voltage and power
Current: time rate of change of electric charge
I = dq/dt
1 Amp = 1 Coulomb/sec
Voltage: electromotive force or potential, V
1 Volt = 1 Joule/Coulomb = 1 N·m/coulomb
Power: P = I V
1 Watt = 1 Volt·Amp = 1 Joule/sec
ECE201 Lect-1

3. Current, I
Normally we talk about the movement of positive charges although we know that, in general, in metallic conductors current results from electron motion (conventionally positive flow)
The sign of the current indicates the direction of flow
Types of current:
direct current (dc): batteries and some special generators
alternating current (ac): household current which varies with time
ECE201 Lect-1

4. Voltage, V
Voltage is the difference in energy level of a unit charge located at each of two points in a circuit, and therefore, represents the energy required to move the unit charge from one point to the other
ECE201 Lect-1

5. Sign Convention
Passive sign convention : current should enter the positive voltage terminal
Consequence for P = I V
Positive (+) Power: element absorbs power
Negative (-) Power: element supplies power I
Circuit Element – +
ECE201 Lect-1

6. Electrical Analogies (Physical)
ECE201 Lect-1

7. Class Examples Learning Extension E1.1 Learning Extension E1.2
ECE201 Lect-1

8. Active vs. Passive Elements
Active elements can generate energy
Batteries
Voltage and current sources
Passive elements cannot generate energy
Resistors
Capacitors and Inductors (but CAN store energy)
ECE201 Lect-1

9. Independent vs. Dependent Sources
An independent source (voltage or current) may be DC (constant) or time-varying, but does not depend on other voltages or currents in the circuit.
The dependent source magnitude is a function of another voltage or current in the circuit. + –
ECE201 Lect-1

10. Dependent Voltage Sources
6Vx
6000Ix + – + –
Voltage Controlled Voltage Source
Current Controlled Voltage Source
ECE201 Lect-1

11. Dependent Current Sources
0.006Vx
6Ix
Voltage Controlled Current Source
Current Controlled Current Source
ECE201 Lect-1

12. Class Examples Learning Extension E1.3 Learning Extension E1.4(a)
ECE201 Lect-1