Power and resonance in ac circuits

Chapter Power and resonance in ac circuits

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • 17CHAPTERPower and resonance inac circuitsYOU HAVE LEARNED HOW CURRENT, VOLTAGE, AND RESISTANCE BEHAVE IN ac circuits. How can all this theoretical knowledge be put to practical use?One of the engineer’s biggest challenges is the problem of efficient energy transfer.This is a major concern at radio frequencies. But audio design engineers, and even theutility companies, need to be concerned with ac circuit efficiency because it translatesinto energy conservation. The first two-thirds of this chapter is devoted to this subject.Another important phenomenon, especially for the radio-frequency engineer, isresonance. This is an electrical analog of the reverberation you’re familiar with if you’veever played a musical instrument. The last third of this chapter discusses resonance inseries and parallel circuits.What is power?There are several different ways to define power. The applicable definition depends onthe kind of circuit or device in use.Energy per unit timeThe most all-encompassing definition of power, and the one commonly used by physi-cists, is this: Power is the rate at which energy is expended. The standard unit ofpower is the watt, abbreviated W; it is equivalent to one joule per second.This definition can be applied to motion, chemical effects, electricity, radio waves,sound, heat, light, ultraviolet, and X rays. In all cases, the energy is “used up” somehow,converted from one form into another form at a certain rate. This expression of powerrefers to an event that takes place at some definite place or places.Sometimes power is given as kilowatts (kW or thousands of watts), megawatts (MWor millions of watts) or gigawatts (GW or billions of watts). It might be given as milliwatts305Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.