1. Lect1EEE 2021 Introduction; Circuit Elements; Ohm's Law; KCL Dr. Holbert January 14, 2008

2. Lect1EEE 2022 Introduction Syllabus: textbook, homework, grading, schedule, reading assignments, laboratory Lectures: let’s avoid “Death by PowerPoint”

3. Lect1EEE 2023 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

4. Lect1EEE 2024 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 I(t)

5. Lect1EEE 2025 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 Circuit Element(s) +– V(t)

6. Lect1EEE 2026 Default 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 Circuit Element + – I

7. Lect1EEE 2027 Electrical Analogies (Physical)

8. Lect1EEE 2028 Active vs. Passive Elements Active elements can generate energy –Voltage and current sources –Batteries Passive elements cannot generate energy –Resistors –Capacitors and Inductors (but CAN store energy)

9. Lect1EEE 2029 Independent Sources An independent source (voltage or current) may be DC (constant) or time-varying (AC), but does not depend on other voltages or currents in the circuit +–+– Voltage Source Current Source

10. Lect1EEE 20210 Resistors A resistor is a circuit element that dissipates electrical energy (usually as heat) Real-world devices that are modeled by resistors: incandescent light bulbs, heating elements (stoves, heaters, etc.), long wires Resistance is measured in Ohms (Ω)

11. Lect1EEE 20211 Ohm’s Law v(t) = i(t) R- or -V = I R p(t) = i 2 (t) R = v 2 (t)/R[+ (absorbing)] v(t)v(t) The Rest of the Circuit R i(t)i(t) + –

12. Lect1EEE 20212 Open Circuit What if R =  ? i(t) = v(t)/R = 0 v(t)v(t) The Rest of the Circuit i(t)=0 + –

13. Lect1EEE 20213 Short Circuit What if R = 0 ? v(t) = R i(t) = 0 The Rest of the Circuit v(t)=0 i(t)i(t) + –

14. Lect1EEE 20214 Series Two elements are in series if the current that flows through one must also flow through the other. R1R1 R2R2 Series R1R1 R2R2 Not Series

15. Lect1EEE 20215 Parallel Two elements are in parallel if they are connected between (share) the same two (distinct) end nodes. ParallelNot Parallel R1R1 R2R2 R1R1 R2R2

16. Lect1EEE 20216 Kirchhoff’s Laws Kirchhoff’s Current Law (KCL) –sum of all currents entering a node is zero –sum of currents entering node is equal to sum of currents leaving node Kirchhoff’s Voltage Law (KVL) –sum of voltages around any loop in a circuit is zero

17. Lect1EEE 20217 KCL (Kirchhoff’s Current Law) The sum of currents entering the node is zero: Analogy: mass flow at pipe junction i1(t)i1(t) i2(t)i2(t)i4(t)i4(t) i5(t)i5(t) i3(t)i3(t)

18. Lect1EEE 20218 Class Examples Drill Problems P1-1, P1-2, P1-4 –While working these problems, we shall define the term ‘node’ as a point where two or more circuit elements are connected