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The Experimental and Historical Foundations of Electricity Volume 2 Andre Koch Torres Assis Apeiron Montreal Published by C. Roy Keys Inc. 4405, rue St-Dominique Montreal, Quebec H2W 2B2 Canada http://redshift.vif.com © André Koch Torres Assis 2018 First Published 2018 Library and Archives Canada Cataloguing in Publication Assis, André Koch Torres, 1962-, author The experimental and historical foundations of electricity / Andre Koch Torres Assis. Issued in print and electronic formats. Includes bibliographical references. ISBN 978-1-987980-10-3 (v. 2 : softcover).--ISBN 978-1-987980-11-0 (v. 2 : PDF) 1. Electricity--Experiments. 2. Electricity--History. I. Title. QC533.A88 2010 537'.078 C2010-901025-6 C2018-901453-9 Front cover: One of the first representations of the Leyden jar experi- ment (1745). Source: A. P. Deschanel, Elementary Treatise on Natural Philosophy. D. Appleton and Co., New York, 1876. Part 3, p. 570, Figure 382. Translated by J. D. Everett. THE EXPERIMENTAL AND HISTORICAL FOUNDATIONS OF ELECTRICITY Volume 2 ANDRE KOCH TORRES ASSIS Institute of Physics University of Campinas—UNICAMP 13083-859 Campinas, SP, Brazil E-mail: assis@ifi.unicamp.br Homepage: www.ifi.unicamp.br/~assis c Andre Koch Torres Assis 2 Contents Presentation and Acknowledgements 9 1 Introduction 13 1.1 The Amber Effect .......................... 13 1.2 The Triboelectric Series ....................... 15 1.2.1 The Position of Water in the Triboelectric Series . 15 1.3 Simple and Primitive Facts about Electricity ........... 17 1.3.1 We Are Not Explaining These Facts, They Were Only Listed ............................. 21 1.3.2 The Meanings of Some Expressions ............ 22 2 Electric Instruments 25 2.1 List of Materials for the Experiments ............... 25 2.2 The Electroscope: The Most Important Instrument of Electro- statics ................................. 26 2.2.1 Main Components of an Electroscope ........... 28 2.2.2 Comparison between the Gold Leaf Electroscope and the Electroscope Made with Low Cost Material . 29 2.2.3 The Electroscope and the Discovery of Cosmic Rays . 30 2.3 The Versorium ............................ 30 2.3.1 The Metal Versorium Supported on a Pin ......... 31 2.3.2 The Metal Versorium Supported on a Pointed Piece of Plastic ............................ 31 2.3.3 The Plastic Versorium ................... 31 2.3.4 The Versorium of Du Fay .................. 32 2.3.5 Main Components of These Versoria ............ 33 2.4 The Electric Pendulum ....................... 33 2.4.1 The Classic Electric Pendulum ............... 34 2.4.2 The Arrow Pendulum .................... 34 2.4.3 The Plastic Pendulum ................... 35 2.4.4 Main Components of These Pendulums .......... 35 2.5 Gray’s Pendulous Thread ...................... 35 2.6 Charge Collectors .......................... 36 2.7 Circuit Tester ............................ 38 3 3 Conductors and Insulators 41 3.1 Classifying Substances as Conductors or Insulators with the Elec- troscope ............................... 41 3.1.1 Definition of Conductor and Insulator when a High Volt- age is Applied between the Ends of the Body . 44 3.1.2 Bodies which Behave as Conductors or Insulators in the Usual Experiments of Electrostatics ............ 45 3.2 Classifying Substances as Conductors or Insulators with the Cir- cuit Tester .............................. 50 3.2.1 Definition of Conductor and Insulator when a Low Poten- tial Difference is Applied between the Ends of the Body . 52 3.2.2 Bodies which Behave as Conductors or Insulators in the Usual Experiments with Constant Current . 52 3.3 Factors Influencing the Conducting and Insulating Properties of a Substance ............................. 54 3.3.1 Nature or Chemical Composition of the Substance . 54 3.3.2 Potential Difference between the Ends of the Body . 54 3.3.3 The Time Required to Discharge an Electrified Body . 55 3.3.4 The Length of the Body .................. 55 3.3.5 The Cross-Sectional Area of the Body ........... 60 3.3.6 Humidity ........................... 66 3.3.7 Orientation of the Body Relative to the Applied Voltage 68 3.3.8 Temperature ......................... 71 3.3.9 Illumination ......................... 71 3.3.10 Other Factors ........................ 72 3.4 Laws Related to Electric Circuits Carrying Steady Currents . 72 4 Conductors and Insulators in Some Simple Experiments 75 4.1 Conductors and Insulators in the Amber Effect .......... 75 4.1.1 Explanation of the Amber Effect in the Textbooks . 75 4.1.2 Our Explanation of the Amber Effect ........... 77 4.1.3 It is Important to Present a Detailed Explanation of the Amber Effect ......................... 80 4.2 Conductors and Insulators in the Experiment of the Attraction of a Stream of Water ........................ 81 4.2.1 Explanation of the Attraction of a Stream of Water in the Textbooks .......................... 81 4.2.2 Our Explanation of the Attraction of a Stream of Water 82 4.2.3 It is Important to Present a Detailed Explanation of the Attraction of a Stream of Water .............. 84 4.3 Differences between Old and Modern Glasses ........... 85 4.3.1 Conducting or Insulating Behavior ............. 86 4.3.2 Density of the Surface Charges Acquired by Friction . 87 4.3.3 The Sign of the Charges Acquired by Rubbed Glass . 88 4.3.4 The Glass in Modern Textbooks and the Importance to Correct What They Say .................. 90 4 4.4 The ACR Mechanism ........................ 91 4.4.1 Explanation of the ACR Mechanism ........... 94 4.4.2 Situations where the ACR Mechanism Does Not Take Place ............................. 95 4.5 The Importance of Stephen Gray’s Discovery of Conductors and Insulators ............................... 97 5 Electrification of Adhesive Tapes 101 5.1 Insulating or Conducting Behavior of the Tape ..........101 5.2 Electrification of the Tape .....................105 5.3 Neutralization of the Tape .....................108 5.4 Electrifying Tapes with Opposite Charges .............110 5.5 Electric Dipoles ...........................112 5.6 General Aspects Related to Adhesive Tapes ............116 6 The Electrophorus 117 6.1 The Instrument ...........................117 6.2 Operation of the Electrophorus ...................118 6.3 A Personal Account .........................123 7 Distribution of Charges in a Conductor 125 7.1 Distribution of Charges in Conductors ...............125 7.1.1 Experiments with Electroscopes ..............125 7.1.2 Collecting the Charges Located on the Internal and Ex- ternal Walls of an Electrified Conductor .........128 7.1.3 Gray, Franklin and the Distribution of Charges on Elec- trified Conductors ......................132 7.1.4 Electrified Conductors Touching the Internal and Exter- nal Walls of Another Conductor ..............135 7.1.5 Distribution of Charges in Open and Closed Conductors 139 7.2 Charges Induced on the Internal and External Walls of a Hollow Conductor ..............................139 7.3 Actions Exerted by a Hollow Electrified Conductor on Internal and External Bodies .........................142 7.4 Faraday’s Ice Pail Experiment ...................143 8 Electric Shielding 147 8.1 Placing a Conductor or an Insulator between an Electrified Body and a Light Body ..........................147 8.1.1 Some Old Research on Screening ..............150 8.2 Experiments with Hollow Conductors ...............152 8.3 Sufficient Conditions for Effective Shielding ............155 8.4 Faraday Cage ............................161 5 9 The Power of Points 163 9.1 Illustrating the Power of Points with Electroscopes ........163 9.2 Collecting and Comparing the Surface Charge Densities . 165 9.3 Gray and the Power of Points ...................169 9.4 Intensifying the Amber Effect ...................173 10 Electrical Equilibrium and the Instrument which Indicates Po- tential Difference 175 10.1 Conductor in Electrical Equilibrium ................175 10.2 The Electric Potential of a Conductor ...............177 10.3 Electroscope with Conducting Case ................178 10.4 Experiments Utilizing the Electroscope with Conducting Case . 183 10.4.1 The Electroscope Shows that All Portions of a Conductor in Equilibrium Are at the Same Potential .........183 10.4.2 Procedures which can Change the Potential of One Con- ductor Relative to the Potential of Another Conductor . 187 10.5 Kelvin and the Electrometer to Measure Potential Difference . 191 11 Electric Discharges in Air 195 11.1 Sparks ................................195 11.2 Comments on These Experiments .................200 11.3 Lightning Rods ...........................201 11.4 Lightning Rod Insulated from the Ground ............203 11.5 Sparks in the ACR Mechanism ...................204 11.6 Neon Lamp ..............................205 11.7 Gray, Franklin, the Power of Points and the Electric Nature of Lightning ...............................207 11.8 Applications of the Power of Points ................214 12 The Leyden Jar and Capacitors 217 12.1 Building a Capacitor ........................217 12.1.1 Do Not Utilize a Glass Bottle in Order to Insulate the Internal Conductor from the External Conductor . 219 12.2 Experiments with the Capacitor ..................220 12.3 Working Mechanism of the Capacitor ...............226 12.4 Gray, Du Fay and the Electrification of Water ..........227 12.5 The First Capacitors or Condensers ................233 13 Temporal Preservation of the Electrification of Bodies 241 13.1 Discharge through the Air .....................241 13.2 Preserving the Electrification of Insulators ............242 13.2.1 Some Comments on These Experiments
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