Electricity and magnetism

Electricity and Magnetism Benjamin Crowell Book in the Light and Matter series of introductory physics textbooks www.lightandmatter.com Electricity and Magnetism The Light and Matter series of introductory physics textbooks: Newtonian Physics Conservation Laws Vibrations and Waves Electricity and Magnetism Optics The Modern Revolution in Physics Electricity and Magnetism Benjamin Crowell www.lightandmatter.com Light and Matter Fullerton, California www.lightandmatter.com © 1999-2002 by Benjamin Crowell All rights reserved Edition 2.1 rev 2002-01-27 ISBN 0-9704670-4-4 To Arnold Arons Brief Contents Electricity and the Atom 15 The Nucleus 41 Circuits, Part 71 Circuits, Part 95 Fields of Force 109 Electromagnetism 127 Exercises 147 Solutions 153 Glossary 155 Index 157 Contents Contents Preface 13 Electricity and the Atom .15 1.1 The Quest for the Atomic Force 16 1.2 Charge, Electricity and Magnetism 18 1.3 Atoms 22 1.4 Quantization of Charge 28 1.5 The Electron 31 1.6 The Raisin Cookie Model of the Atom 35 Summary 37 Homework Problems 38 Circuits, Part 71 3.1 3.2 3.3 3.4 3.5 Current 72 Circuits 75 Voltage 76 Resistance 80 Current-Conducting Properties of Materials 87 3.6∫ Applications of Calculus 90 Summary 91 Homework Problems 92 The Nucleus .41 2.1 2.2 2.3 2.4 2.5 Radioactivity 41 The Planetary Model of the Atom 45 Atomic Number 48 The Structure of Nuclei 52 The Strong Nuclear Force, Alpha Decay and Fission 56 2.6 The Weak Nuclear Force; Beta Decay 58 2.7 Fusion 61 2.8 Nuclear Energy and Binding Energies 62 2.9 Biological Effects of Ionizing Radiation 65 2.10* The Creation of the Elements 67 Summary 69 Homework Problems 70 10 Contents Circuits, Part 95 4.1 Schematics 96 4.2 Parallel Resistances and the Junction Rule 97 4.3 Series Resistances 101 Summary 105 Homework Problems 106 K Keynes, John Maynard 16 L light defined 24 loop rule 102 in series 101 resistivity defined 102 resistor 84 resistors in parallel 97 S magnetic field 126 defined 127 magnetostatics 128 mass conservation of 22 matter defined 24 Maxwell, James Clerk 132 Mendeleev, Dmitri 26 Millikan, Robert 28 millirem (unit) 65 moment dipole 116 monopoles magnetic 126 schematic 96 schematics 96 scholasticism 23 sea-of-arrows representation 113 series circuit defined 86 short circuit defined 83 sinks in fields 113 solenoid 129 sources of fields 113 special relativity 63 spectrum electromagnetic 135 strong nuclear force 56 superposition of fields 113 symmetry 140 N T neutral (electrically) 19 Newton 130 Newton, Isaac 15 nuclear forces 56, 140 nucleus discovery 46 tesla (unit) 127 Thomson, J.J cathode ray experiments 32 transformer 133 M Urban, Pope 23 O V ohmic defined 81 open circuit 75 volt (unit) defined 76 voltage related to electric field 118 P parallel circuit defined 86 polarization 134 Q quantization 28 R radar 125 raisin cookie model 35 rem (unit) 65 resistance defined 80 in parallel 97 160 U Index W waves electromagnetic 134 gravitational 114 weak nuclear force 58, 140 Index 161 162 Index Photo Credits All photographs are by Benjamin Crowell, except as noted below Credits marked with an asterisk are photographs or illustrations from the turn of the 20th century whose copyrights have expired Cover Cat neuron: Courtesy of Richard J Harris, University of Western Ontario Accelerator: Courtesy of A Zachau, GSI Chapter Lightning: C Clark/NOAA photo library, uncopyrighted J.J Thomson: Harper’s Monthly, 1904.* Millikan’s apparatus: Caltech.* Robert Millikan: Clark Millikan, 1891.* Chapter Curies: Harper’s Monthly, 1904.* GAMMASPHERE: C.J Lister/R.V.F Janssens, uncopyrighted Chapter Knifefish: Courtesy of Greg DeGreef Superconducting accelerator segment: Courtesy of Argonne National Laboratory, managed and operated by the University of Chicago for the U.S Department of Energy under contract No W-31-109-ENG-38 Chapter Radar: U.S Forestry Service © 1998 Benjamin Crowell 163 164 165 166 167 168 169 170 171 172 173 Useful Data Metric Prefixes Mmega106 kkilo103 mmilli10 –3 µ- (Greek mu) micro10 –6 nnano10 –9 ppico10 –12 ffemto10 –15 -2 (Centi-, 10 , is used only in the centimeter.) Notation and Units quantity distance time mass density force velocity acceleration energy momentum angular momentum period wavelength frequency charge current voltage (potential) resistance electric field magnetic field unit symbol meter, m x, ∆x second, s t, ∆t kilogram, kg m kg/m3 ρ newton, N=1 kg.m/s2 F m/s v m/s2 a joule, J E kg.m/s p kg.m2/s L s T m λ s-1 or Hz f coulomb, C q ampere, A I volt, V V ohm, Ω R N/C E tesla, T=1 N.s/C.m B Fundamental Constants gravitational constant Coulomb constant quantum of charge speed of light magnetic field constant 174 G=6.67x10 –11 N.m2/kg2 k=8.99x109 N.m2/C2 e=1.60x10 –19 C c=3.00x108 m/s µo=4πx10–7 T.m/A Conversions Conversions between SI and other units: inch = 2.54 cm (exactly) mile = 1.61 km pound = 4.45 N = 2.2 lb (1 kg) g gallon = 3.78x103 cm3 horsepower = 746 W kcal* = 4.18x103 J *When speaking of food energy, the word “Calorie” is used to mean kcal, i.e 1000 calories In writing, the capital C may be used to indicate Calorie=1000 calories Conversions between U.S units: foot = 12 inches yard = feet mile = 5280 ft Earth, Moon, and Sun body mass (kg) radius (km)radius of orbit (km) earth 5.97x1024 6.4x103 1.49x108 moon 7.35x1022 1.7x103 3.84x105 30 sun 1.99x10 7.0x10 The radii and radii of orbits are average values The moon orbits the earth and the earth orbits the sun Subatomic Particles particle mass (kg) charge radius (fm) electron 9.109x10-31 –e