GEORGE WESTINGHOUSE ( – ) George Westinghouse ( – ) A leading proponent of the use of alternating current over direct current. Thus, he came into conflict with Thomas Alva Edison, an advocate of direct current. Westinghouse was convinced that the technology of alternating current was the key to the electrical future. He founded the famous Company named after him and enlisted the services of Nicola Tesla and other inventors in the development of alternating current motors and apparatus for the transmission of high tension current, pioneering in large scale lighting.
not mean that the average power consumed is zero and that there is no dissipation of electrical energy. As you know, Joule heating is given by i R and depends on i (which is always positive whether i is positive or negative) and not on i . Thus, there is Joule heating and dissipation of electrical energy when an ac current passes through a resistor. The instantaneous power dissipated in the resistor is sin p i R i R ( .
) The average value of p over a cycle is * sin p i R i R = < > = < > [ . (a)] where the bar over a letter(here, p ) denotes its average value and <......> denotes taking average of the quantity inside the bracket. Since, i m and R are constants, sin p i R < > [ . (b)] Using the trigonometric identity, sin ω t = / ( – cos ω t ), we have < sin ω t > = ( / ) ( – < cos ω t > ) and since < cos2 ω t > = ** , we have, sin < > = Thus, p i R [ .
(c)] To express ac power in the same form as dc power ( P = I R ), a special value of current is defined and used. It is called, root mean square (rms) or effective current (Fig. . ) and is denoted by I rms or I .
* The average value of a function F ( t ) over a period T is given by ( ) ( ) T F t F t T