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CHAPTER 2: COULOMB'S LAW AND ELECTRIC FIELD INTENSITY

Bây giờ chúng ta đã xây dựng một ngôn ngữ mới trong chương đầu tiên, chúng ta sẽ thiết lập một vài nguyên tắc cơ bản của điện và cố gắng để mô tả chúng trong các điều khoản của nó. | CHAPTER 2 COULOMB S LAW AND ELECTRIC FIELD INTENSITY Now that we have formulated a new language in the first chapter we shall establish a few basic principles of electricity and attempt to describe them in terms of it. If we had used vector calculus for several years and already had a few correct ideas about electricity and magnetism we might jump in now with both feet and present a handful of equations including Maxwell s equations and a few other auxiliary equations and proceed to describe them physically by virtue of our knowledge of vector analysis. This is perhaps the ideal way starting with the most general results and then showing that Ohm s Gauss s Coulomb s Faraday s Ampere s Biot-Savart s Kirchhoffs and a few less familiar laws are all special cases of these equations. It is philosophically satisfying to have the most general result and to feel that we are able to obtain the results for any special case at will. However such a jump would lead to many frantic cries of Help and not a few drowned students. Instead we shall present at decent intervals the experimental laws mentioned above expressing each in vector notation and use these laws to solve a 27 I e-Text Main Menu Textbook Table of Contents 28 ENGINEERING ELECTROMAGNETICS number of simple problems. In this way our familiarity with both vector analysis and electric and magnetic fields will gradually increase and by the time we have finally reached our handful of general equations little additional explanation will be required. The entire field of electromagnetic theory is then open to US and we may use Maxwell s equations to describe wave propagation radiation from antennas skin effect waveguides and transmission lines and travelling-wave tubes and even to obtain a new insight into the ordinary power transformer. In this chapter we shall restrict our attention to static electric fields in vacuum or free space. Such fields for example are found in the focusing and deflection systems of electrostatic .