Alternating current basics

Chapter Alternating current basics

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

  • 9CHAPTERAlternating currentbasicsDIRECT CURRENT (DC) IS SIMPLE. IT CAN BE EXPRESSED IN TERMS OF JUST TWOvariables: polarity (or direction), and magnitude. Alternating current (ac) is somewhatmore complicated, because there are three things that can vary. Because of the greaternumber of parameters, alternating-current circuits behave in more complex ways thandirect-current circuits. This chapter will acquaint you with the most common forms ofalternating current. A few of the less often-seen types are also mentioned.Definition of alternating currentRecall that direct current has a polarity, or direction, that stays the same over a long pe-riod of time. Although the magnitude might vary—the number of amperes, volts, orwatts can fluctuate—the charge carriers always flow in the same direction through thecircuit.In alternating current, the polarity reverses again and again at regular intervals.The magnitude usually changes because of this constant reversal of polarity, althoughthere are certain cases where the magnitude doesn’t change even though the polaritydoes.The rate of change of polarity is the third variable that makes ac so much differentfrom dc. The behavior of an ac wave depends largely on this rate: the frequency.Period and frequencyIn a periodic ac wave, the kind that is discussed in this chapter (and throughout the restof this book), the function of magnitude versus time repeats itself over and over, so thatthe same pattern recurs countless times. The length of time between one repetition of thepattern, or one cycle, and the next is called the period of the wave. This is illustrated in165Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.