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1.1 Introduction * Objectives * Requirements & Grading Policy * Other information

Lecture 1. Getting Started. 1.1 Introduction * Objectives * Requirements & Grading Policy * Other information 1.2 Basic Circuit Concepts * Electrical quantities

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1.1 Introduction * Objectives * Requirements & Grading Policy * Other information

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  1. Lecture 1. Getting Started 1.1 Introduction * Objectives * Requirements & Grading Policy * Other information 1.2 Basic Circuit Concepts * Electrical quantities  current, voltage & power, sign conventions * Circuit elements Passive, active and sources * Basic laws Ohm’s law and Kirchhoff’s laws

  2. EEE 202: Circuits 1, Spring 2008 Prerequisite EEE 101 Pre- or co-requisites: MAT 274 or MAT 275, PHY 131, 132. Instructor: Dr. NJ Tao (njtao@asu.edu) Where: Schwada Classroom & Office 150 When: Tu and Th 3:15-4:30 pm Office Hours: Tu and Th 2:00 - 3:00 p.m. or by appointment. Office Location: GWC618 Class Website: http://www.public.asu.edu/~ntao1/Teaching/ECE202/EEE202web.htm

  3. 1.2. Basic Circuit Concepts * Electrical quantities  current, voltage & power, sign conventions * Circuit elements Passive, active and sources * Basic laws Ohm’s law and Kirchhoff’s laws

  4. Electrical Quantities • Basic quantities: • Current (I): time rate of change of electric charge I = dq/dt Unit: 1 Amp = 1 Coulomb/sec • Voltage (V): electromotive force or potential Unit: 1 Volt = 1 Joule/Coulomb = 1 N·m/coulomb • Power (P): rate at which work is done P = IV 1 Watt = 1 Volt·Amp = 1 Joule/sec

  5. Water Analogy

  6. I(t) Current, I • The sign of the current indicates the direction of flow • Current due to positive & negative charge carried; the moving direction of positive charge is conventionally defined as direct of current. What are charge carries in copper wire, Silicon and salt solution? • DC & AC currents: • direct current (dc): batteries and some special generators • alternating current (ac): household current which varies with time

  7. Circuit Element(s) + – V(t) Voltage, V • Voltage is the difference in electrical potentials between, e.g., two points in a circuit; it is the energy required to move an unit charge from one point to the other. • Voltage with respect to a common point or “ground”. • Positive (high) and negative (low) voltages. What is electrical potential?

  8. I Circuit Element – + Default Sign Convention • Passive sign convention : current should enter the positive voltage terminal • Passive sign convention: P = I V • Positive (+) Power: element absorbs power • Negative (-) Power: element supplies power

  9. 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)

  10. + – 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

  11. 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)

  12. i(t) + The Rest of the Circuit R – Ohm’s Law v(t) = i(t) R - or - V = I R p(t) = i2(t) R = v2(t)/R [+ (absorbing)] v(t)

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

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

  15. Resistors in Series Two or more elements are in series if the current that flows through one must also flow through the other. In series R1 R2 I1 = I2 Not in series R1 R2 I1 ≠ I2

  16. R1 R2 Resistors in Parallel • Two or more elements are in parallel if they are connected between (share) the same two (distinct) end nodes; • The voltages across these elements are the same. R1 R2 Parallel Not Parallel

  17. 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 • Conservation of charge • Kirchhoff’s Voltage Law (KVL) • sum of voltages around any loop in a circuit is zero • Conservation of energy

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

  19. Class Examples • Drill Problems 1, 2, 4

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