Fifth Edition, last update October 18, 2006 2 Lessons In Electric Circuits, Volume I – DC By Tony R. Kuphaldt Fifth Edition, last update October 18, 2006 i c 2000-2011, Tony R. Kuphaldt This book is published under the terms and conditions of the Design Science License. These terms and conditions allow for free copying, distribution, and/or modification of this document by the general public. The full Design Science License text is included in the last chapter. As an open and collaboratively developed text, this book is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the Design Science License for more details. Available in its entirety as part of the Open Book Project collection at: openbookproject.net/electricCircuits PRINTING HISTORY • First Edition: Printed in June of 2000. Plain-ASCII illustrations for universal computer readability. • Second Edition: Printed in September of 2000. Illustrations reworked in standard graphic (eps and jpeg) format. Source files translated to Texinfo format for easy online and printed publication. • Third Edition: Equations and tables reworked as graphic images rather than plain-ASCII text. • Fourth Edition: Printed in August 2001. Source files translated to SubML format. SubML is a simple markup language designed to easily convert to other markups like LATEX, HTML, or DocBook using nothing but search-and-replace substitutions. • Fifth Edition: Printed in August 2002. New sections added, and error corrections made, since the fourth edition. ii Contents 1 BASIC CONCEPTS OF ELECTRICITY 1 1.1 Static electricity ..................................... 1 1.2 Conductors, insulators, and electron flow ....................... 8 1.3 Electric circuits ...................................... 12 1.4 Voltage and current ................................... 14 1.5 Resistance ......................................... 23 1.6 Voltage and current in a practical circuit ....................... 28 1.7 Conventional versus electron flow ........................... 29 1.8 Contributors ........................................ 33 2 OHM’s LAW 35 2.1 How voltage, current, and resistance relate ...................... 35 2.2 An analogy for Ohm’s Law ................................ 40 2.3 Power in electric circuits ................................. 42 2.4 Calculating electric power ................................ 44 2.5 Resistors .......................................... 46 2.6 Nonlinear conduction .................................. 51 2.7 Circuit wiring ....................................... 57 2.8 Polarity of voltage drops ................................. 60 2.9 Computer simulation of electric circuits ........................ 61 2.10 Contributors ........................................ 76 3 ELECTRICAL SAFETY 77 3.1 The importance of electrical safety ........................... 77 3.2 Physiological effects of electricity ............................ 78 3.3 Shock current path .................................... 80 3.4 Ohm’s Law (again!) .................................... 86 3.5 Safe practices ....................................... 93 3.6 Emergency response ................................... 96 3.7 Common sources of hazard ............................... 98 3.8 Safe circuit design .................................... 100 3.9 Safe meter usage ..................................... 106 3.10 Electric shock data .................................... 116 3.11 Contributors ........................................ 117 iii iv CONTENTS Bibliography ........................................... 117 4 SCIENTIFIC NOTATION AND METRIC PREFIXES 119 4.1 Scientific notation .................................... 119 4.2 Arithmetic with scientific notation ........................... 121 4.3 Metric notation ...................................... 123 4.4 Metric prefix conversions ................................ 124 4.5 Hand calculator use ................................... 125 4.6 Scientific notation in SPICE .............................. 126 4.7 Contributors ........................................ 128 5 SERIES AND PARALLEL CIRCUITS 129 5.1 What are ”series” and ”parallel” circuits? ....................... 129 5.2 Simple series circuits ................................... 132 5.3 Simple parallel circuits ................................. 139 5.4 Conductance ........................................ 144 5.5 Power calculations .................................... 146 5.6 Correct use of Ohm’s Law ................................ 147 5.7 Component failure analysis ............................... 149 5.8 Building simple resistor circuits ............................ 155 5.9 Contributors ........................................ 170 6 DIVIDER CIRCUITS AND KIRCHHOFF’S LAWS 171 6.1 Voltage divider circuits .................................. 171 6.2 Kirchhoff’s Voltage Law (KVL) ............................. 179 6.3 Current divider circuits ................................. 190 6.4 Kirchhoff’s Current Law (KCL) ............................. 193 6.5 Contributors ........................................ 196 7 SERIES-PARALLEL COMBINATION CIRCUITS 197 7.1 What is a series-parallel circuit? ............................ 197 7.2 Analysis technique .................................... 200 7.3 Re-drawing complex schematics ............................ 208 7.4 Component failure analysis ............................... 216 7.5 Building series-parallel resistor circuits ........................ 221 7.6 Contributors ........................................ 233 8 DC METERING CIRCUITS 235 8.1 What is a meter? ..................................... 235 8.2 Voltmeter design ..................................... 241 8.3 Voltmeter impact on measured circuit ......................... 246 8.4 Ammeter design ..................................... 253 8.5 Ammeter impact on measured circuit ......................... 260 8.6 Ohmmeter design ..................................... 264 8.7 High voltage ohmmeters ................................. 269 8.8 Multimeters ........................................ 277 CONTENTS v 8.9 Kelvin (4-wire) resistance measurement ....................... 282 8.10 Bridge circuits ....................................... 289 8.11 Wattmeter design ..................................... 296 8.12 Creating custom calibration resistances ........................ 297 8.13 Contributors ........................................ 300 9 ELECTRICAL INSTRUMENTATION SIGNALS 301 9.1 Analog and digital signals ................................ 301 9.2 Voltage signal systems .................................. 304 9.3 Current signal systems ................................. 306 9.4 Tachogenerators ..................................... 309 9.5 Thermocouples ...................................... 310 9.6 pH measurement ..................................... 315 9.7 Strain gauges ....................................... 321 9.8 Contributors ........................................ 328 10 DC NETWORK ANALYSIS 329 10.1 What is network analysis? ................................ 329 10.2 Branch current method ................................. 332 10.3 Mesh current method .................................. 341 10.4 Node voltage method .................................. 357 10.5 Introduction to network theorems ........................... 361 10.6 Millman’s Theorem .................................... 361 10.7 Superposition Theorem ................................. 364 10.8 Thevenin’s Theorem ................................... 369 10.9 Norton’s Theorem ..................................... 373 10.10Thevenin-Norton equivalencies ............................. 377 10.11Millman’s Theorem revisited .............................. 379 10.12Maximum Power Transfer Theorem .......................... 381 10.13∆-Y and Y-∆ conversions ................................ 383 10.14Contributors ........................................ 389 Bibliography ........................................... 390 11 BATTERIES AND POWER SYSTEMS 391 11.1 Electron activity in chemical reactions ........................ 391 11.2 Battery construction ................................... 397 11.3 Battery ratings ...................................... 400 11.4 Special-purpose batteries ................................ 402 11.5 Practical considerations ................................. 406 11.6 Contributors ........................................ 408 Bibliography ........................................... 408 vi CONTENTS 12 PHYSICS OF CONDUCTORS AND INSULATORS 409 12.1 Introduction ........................................ 409 12.2 Conductor size ...................................... 411 12.3 Conductor ampacity ................................... 417 12.4 Fuses ............................................ 419 12.5 Specific resistance .................................... 427 12.6 Temperature coefficient of resistance ......................... 431 12.7 Superconductivity .................................... 434 12.8 Insulator breakdown voltage .............................. 436 12.9 Data ............................................ 438 12.10Contributors ........................................ 438 13 CAPACITORS 439 13.1 Electric fields and capacitance ............................. 439 13.2 Capacitors and calculus ................................. 444 13.3 Factors affecting capacitance .............................. 449 13.4 Series and parallel capacitors .............................. 452 13.5 Practical considerations