# BASIC AC THEORY

### Chapter 1 BASIC AC THEORY

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### Lessons In Electric Circuits Volume II – AC Book

• Chapter 1BASIC AC THEORYContents 10,1.1 10,What 10,is 10,alternating 10,current 10,(AC)?. . . . . . . . . . . . . . . . . . . .1 15,1.2 15,AC 15,waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 20,1.3 20,Measurements 20,of 20,AC 20,magnitude . . . . . . . . . . . . . . . . . . . . . .11 27,1.4 27,Simple 27,AC 27,circuit 27,calculations . . . . . . . . . . . . . . . . . . . . . . .18 29,1.5 29,AC 29,phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 31,1.6 31,Principles 31,of 31,radio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 33,1.7 33,Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .241.1What is alternating current (AC)?Most students of electricity begin their study with what is known as direct current (DC), which iselectricity ﬂowing in a constant direction, and/or possessing a voltage with constant polarity. DCis the kind of electricity made by a battery (with deﬁnite positive and negative terminals), or thekind of charge generated by rubbing certain types of materials against each other.As useful and as easy to understand as DC is, it is not the only “kind” of electricity in use. Certainsources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltagesalternating in polarity, reversing positive and negative over time. Either as a voltage switchingpolarity or as a current switching direction back and forth, this “kind” of electricity is known asAlternating Current (AC): Figure 11,1.1Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, thecircle with the wavy line inside is the generic symbol for any AC voltage source.One might wonder why anyone would bother with such a thing as AC. It is true that in somecases AC holds no practical advantage over DC. In applications where electricity is used to dissipateenergy in the form of heat, the polarity or direction of current is irrelevant, so long as there isenough voltage and current to the load to produce the desired heat (power dissipation). However,with AC it is possible to build electric generators, motors and power distribution systems that are1