ABSTRACT
It is difficult to think of any technological systems of medium or large scale which do not involve electricity in some way. If, however, we restrict our consideration to cases in which system functions are performed largely by electrical means the following examples might come to mind:
I. Electrical power transmission and distribution 2. Communications (cable, radio, television, microwave, etc.) 3. General-purpose computers 4. Electro-optics (optoelectronics?) (lasers, fiber optics, imaging systems, etc.)
Application areas which, in general, are electromechanical, electrothermal, electromechano-acoustic, etc., but which might in specific cases be largely electrical include:
I. Measurement systems 2. Control systems
We described mechanical elements in terms of their force/motion relations. The electrical components or elements of this chapter will be described in terms of their voltage/current relations. To dispel some incorrect but common word usage, note that an "electric" motor is not an electrical device but rather an electromechanical one, since its description requires specification of not just voltage/current relations but also force/motion relations. The useful aspect of an "electric" motor is that it can perform mechanical work. Similarly, a phototransistor (transistor sensitive to light) is an electro-optical device, since its description involves voltage, current, and light flux. A loudspeaker would be an electro-mechano-acoustic device while a microphone would be acousto-mechano-electrical. Such "mixed-media" devices are extremely important in many systems, but since they are not strictly electrical we do not include them in this chapter. Some of the more important ones will be treated briefly in Chap. 5, Basic Energy Converters.
