2 - Electric circuit elements

Abstract

This chapter describes the different aspects of the electric circuit elements. Circuit elements are said to be either active or passive and the elements which make up a circuit include a voltage or a current source of energy, and resistors, inductors, and capacitors. There are two basic variables in electric circuits—namely, electric current, and electric potential difference. A source of energy is required to cause a current to flow and, thereby to produce electric voltages in various parts of the circuit. The electric potential difference between two points is defined as being the work required to move a unit positive charge between them. Materials within which charges can move easily are called conductors. Examples of good conductors are copper and aluminum, in which electrons can move easily but cannot easily move away from the surface and out of the metal. These materials are said to have a low resistance. Virtually all devices and equipment have inherent resistance. A circuit element designed specifically to have resistance is called a resistor. There are two circuit symbols commonly used for resistance and either is perfectly acceptable. A resistor which does not obey Ohm's law—that is, one for which the graph of voltage across it to a base of current through it is not a straight line—is said to be nonlinear. The variation of potential difference across a capacitor is also elaborated in the chapter.