Lecture 1: Intro & Circuit Variables Nilsson , ENG17 : Circuits I Spring March 31, 2015

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 2

Dr. Kyle Montgomery B.S University of Houston 3 Schlumberger M.S Purdue University Ph.D Purdue University –Thesis: Novel Approaches for Wide Bandgap Solar Cells 3

What I do now…besides teach… Advise students Research –Novel solar cells w/compound semiconductors –New materials for lighting, solar cells, and beyond –High speed, high power transistors –Alternative energy storage solutions 4

Philosophy…on teaching…and life Teaching is not confined to classroom time Conceptual understanding is key Life really sucks sometimes…how can I help? 5

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 6

ENG17: Circuits 1 Electrical quantities and elements Resistive Circuits Transient and steady-state responses of RLC circuits Sinusoidal excitation and phasors Complex frequency and network functions Power Calculations 7

Course Structure TAs –Matt Clements –Songjie Bi –Chi Van Pham –Burcu Ercan –Yuhao Liu –Xin Zhao (Tuesday discussions) –Nathan Ellis (Thursday discussions) Course Website is: – –Smartsite used primarily for grades Also using Piazza 8

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 9

SI Units 10

Derived Units 11

Prefixes 12

Examples 13

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 14

Big Picture Need justifies design Design specs filter to concept, circuit model, prototype Circuit analysis necessary for foundation 15

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 16

Voltage 17

Current 18

Ohm’s Law 19

Water Analogy Water pressure = voltage Water flow = current 20

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 21

Ideal Element 22 Passive sign convention

Fundamental Quantities 23 1.Voltage (v) 2.Current (i) 3.Charge (q) 4.Flux (Φ)

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 24

Power ≠ Energy Power = Time Derivative of Energy UNITS! –Power in Watts –Energy in Watt-hrs or Joules Positive Power = Power Delivered to Circuit Negative Power = Power Extracted from Circuit 25

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Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 27

5 Ideal Basic Circuit Elements Voltage Sources Current Sources Resistors Inductors Capacitors 28 “Active Elements” Generate Electric Energy “Passive Elements” Do NOT Generate Electric Energy

Ideal Sources 29 Voltage Source (const. voltage) Current Source (const. current) Circle means “Independent Source”

Dependent Sources 30 Voltage Sources Current Sources Diamond means “Dependent Source”

Schematics 31 Wire Assume No Resistance Node Any defined point (usually a point of intersection) Valid configuration

Schematics (w/dependents) 32 Valid configuration Invalid configuration Valid configuration

Schematics - GND Ground (GND) is a common connection Typically connect to Earth GND Always a zero [V] reference potential 33 GND Connect

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 34

Ohm’s Law 35 Note change in sign Assume ideal resistance (no change w/time)

Conductance 36

Power & Ohm’s Law 37 Therefore… Ohm’s Law Power Relationship or

Examples 38

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 39

Designing a Circuit Model 40

Additional Elements 41 Short Circuit Open Circuit Switch

Schematic V9V Batteries Lamp Case SwitchSpring

Overview Personal Introduction Course Introduction Units Circuit Analysis Voltage / Current Basic Circuit Element Power / Energy Voltage & Current Sources Electrical Resistance Circuit Model Kirchhoff’s Laws 43

The Setup 44 Use common subscripts Establish Reference Polarities Establish Nodes that Connect Elements 7 unknowns…need 7 equations From Ohm’s Law:

Kirchhoff’s Current Law (KCL) 45 The algebraic sum of all the currents at any node in a circuit equals zero. Therefore: Assign signs to currents at each node Positive (+) for current leaving a node Negative (-) for current entering a node Or vice versa

Kirchhoff’s Voltage Law (KVL) 46 The algebraic sum of all the voltages around any closed path in a circuit equals zero. Therefore: Assign signs to voltages in a loop Positive (+) for voltage rise Negative (-) for voltage drop Or vice versa

Observations 7 equations  4 equations –Because I and V are related through R, we only need one With only 2 branches at a node (in series), we only need to know 1 current 47

KCL Example 48

KVL Example 49