1. ece201 lecture 11 Units (1.1) Basic Quantities (1.2) Circuit Elements (1.3) Prof. Phillips January 22, 2003 Introduction

2. ece201 lecture 12 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 Think “FLOW of charges (-e _ )” –Voltage: electromotive force or potential, V 1 Volt = 1 Joule/Coulomb = 1 N·m/coulomb Think “charge (-e _ ) PRESSURE” –Power (dissipated):P = I V 1 Watt = 1 Volt·Amp = 1 Joule/sec

3. ece201 lecture 13 Current, I Current is the movement of positive charges (flow) But usually, in metallic conductors current results from electron motion The sign of the current indicates the direction of flow of positive charges Types of current: –direct current (dc): batteries and some special generators (constant) –alternating current (ac): household current which varies with time (sine wave)

4. ece201 lecture 14 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 A good analogy is pressure for fluids

5. ece201 lecture 15 Sign Convention Passive sign convention : current should enter the positive voltage terminal (flows through the device from + to -, “downhill”) Consequence for P = I V –Positive (+) Power: element absorbs (dissipates) –Negative (-) Power: element supplies power Circuit Element + – I

6. ece201 lecture 16 Electrical Analogies (Physical)

7. ece201 lecture 17 Class Examples

8. ece201 lecture 18 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)

9. ece201 lecture 19 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. +–+– 24V6 cos(t) A

10. ece201 lecture 110 Dependent Voltage Sources +–+– 6Vx6Vx Voltage Controlled Voltage Source 6000I x Current Controlled Voltage Source +–+–

11. ece201 lecture 111 Dependent Current Sources 0.006V x Voltage Controlled Current Source 6Ix6Ix Current Controlled Current Source

12. ece201 lecture 112 Class Examples