Introduction Units 1 1 Basic Quantities 1 2

Introduction; Units (1. 1); Basic Quantities (1. 2); Circuit Elements (1. 3) Dr. Holbert January 18, 2006 ECE 201 Lect-1 1

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=IV 1 Watt = 1 Volt·Amp = 1 Joule/sec ECE 201 Lect-1 2

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 ECE 201 Lect-1 3

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 ECE 201 Lect-1 4

Sign Convention • Passive sign convention : current should enter the positive voltage terminal I + Circuit Element – • Consequence for P = I V – Positive (+) Power: element absorbs power – Negative (-) Power: element supplies power ECE 201 Lect-1 5

Electrical Analogies (Physical) ECE 201 Lect-1 6

Class Examples • Learning Extension E 1. 1 • Learning Extension E 1. 2 ECE 201 Lect-1 7

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) ECE 201 Lect-1 8

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. ECE 201 Lect-1 9

Dependent Voltage Sources + – 6 Vx Voltage Controlled Voltage Source ECE 201 Lect-1 + – 6000 Ix Current Controlled Voltage Source 10

Dependent Current Sources 0. 006 Vx Voltage Controlled Current Source 6 Ix Current Controlled Current Source ECE 201 Lect-1 11

Class Examples • Learning Extension E 1. 3 • Learning Extension E 1. 4(a) • Learning Extension E 1. 5 ECE 201 Lect-1 12