ABSTRACT
Because voltage is induced in a conductor when lines of force are cut, the amount of the induced emf depends on the number of lines cut in a unit of time. To induce an emf of 1 volt, a conductor must cut 100 million lines of force per second. To obtain this great number of "cuttings," the conductor is formed into a loop and is rotated on an axis at great speed (see Figure 6.1). The two sides of the loop become individual conductors in series, each side of the loop cutting lines of force and inducing twice the voltage that a single conductor would induce. In commercial generators, the number of "cuttings" and the resulting emf are increased by (1) increasing the number of lines of force by using more magnets or stronger electromagnets, (2) using more conductors or loops, and (3) rotating the loops faster. (Note: both a-c and d-c generators are covered in Chapter 11.)
How an a-c generator operates to produce an a-c voltage and current is a basic concept today and is taught in elementary and middle school science classes. Of course, we accept technological advances as commonplace, today-we surf the Internet, watch cable television, use our cell phones, and take space flight as a given-and consider producing the electricity that makes all these technologies possible as our right. These technologies are bottom shelf to us today-we have them available to us so we simply use them. This point of view surely was not held initiallyespecially by those who broke ground in developing technology and electricity.
