chapter 04

# chapter 04 - PART 2 ELECTROSTATICS Chapter 4 ELECTROSTATIC...

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PART 2 ELECTROSTATICS

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Chapter 4 ELECTROSTATIC FIELDS Take risks: if you win, you will be happy; if you lose you will be wise. —PETER KREEFT 4.1 INTRODUCTION Having mastered some essential mathematical tools needed for this course, we are now prepared to study the basic concepts of EM. We shall begin with those fundamental con- cepts that are applicable to static (or time-invariant) electric fields in free space (or vacuum). An electrostatic field is produced by a static charge distribution. A typical example of such a field is found in a cathode-ray tube. Before we commence our study of electrostatics, it might be helpful to examine briefly the importance of such a study. Electrostatics is a fascinating subject that has grown up in diverse areas of application. Electric power transmission, X-ray machines, and lightning protection are associated with strong electric fields and will require a knowledge of elec- trostatics to understand and design suitable equipment. The devices used in solid-state electronics are based on electrostatics. These include resistors, capacitors, and active devices such as bipolar and field effect transistors, which are based on control of electron motion by electrostatic fields. Almost all computer peripheral devices, with the exception of magnetic memory, are based on electrostatic fields. Touch pads, capacitance keyboards, cathode-ray tubes, liquid crystal displays, and electrostatic printers are typical examples. In medical work, diagnosis is often carried out with the aid of electrostatics, as incorpo- rated in electrocardiograms, electroencephalograms, and other recordings of organs with electrical activity including eyes, ears, and stomachs. In industry, electrostatics is applied in a variety of forms such as paint spraying, electrodeposition, electrochemical machining, and separation of fine particles. Electrostatics is used in agriculture to sort seeds, direct sprays to plants, measure the moisture content of crops, spin cotton, and speed baking of bread and smoking of meat. 12 'For various applications of electrostatics, see J. M. Crowley, Fundamentals of Applied Electrostat- ics. New York: John Wiley & Sons, 1986; A. D. Moore, ed., Electrostatics and Its Applications. New York: John Wiley & Sons, 1973; and C. E. Jowett, Electrostatics in the Electronics Environment. New York: John Wiley & Sons, 1976. 2 An interesting story on the magic of electrostatics is found in B. Bolton, Electromagnetism and Its Applications. London: Van Nostrand, 1980, p. 2. 103
104 Electrostatic Fields We begin our study of electrostatics by investigating the two fundamental laws gov- erning electrostatic fields: (1) Coulomb's law, and (2) Gauss's law. Both of these laws are based on experimental studies and they are interdependent. Although Coulomb's law is ap- plicable in finding the electric field due to any charge configuration, it is easier to use Gauss's law when charge distribution is symmetrical. Based on Coulomb's law, the concept of electric field intensity will be introduced and applied to cases involving point, line, surface, and volume charges. Special problems that can be solved with much effort

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chapter 04 - PART 2 ELECTROSTATICS Chapter 4 ELECTROSTATIC...

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