During the 1880s in the United States there was a heated and acrimonious between two inventors over the best method of electric-power distribution. Thomas Edison favored direct current (de), that is, steady current that does not vary with time. George Westinghouse favored altering current (ae), with sinusoidal varying voltages and currents. He argued that transformers (which we will study in this chapter) can be used to step the voltage up and down with ac but not with dc; low voltages are safer for consumer use, but high voltages and correspondingly low currents are best for long-distance power transmission to minimize 1 R losses in the cables.
Eventually, Westinghouse prevailed, and most present-day household and industrial power-distribution systems operate with alternating current Any appliance that you plug into a wall outlet uses ac, and many battery-powered devices such as radios and cordless telephones make use of the dc supplied by the battery to create or amplify alternating currents. Circuits in modem communication equipment, including radio and television, also make extensive use of ac.
In this chapter we will learn how resistors, instructors, and capacitors behave in circuits with sinusoidal varying voltages and currents. Many of the principles that we found useful in Chapters 26, 29, and 31 are applicable, along with several new concepts related to the circuit behavior of instructors and capacitors. A key concept in this discussion is resonance, which we studied in Chapter 13 for mechanical systems.