Circuit Principles



Circuit Principles

Resistance

Resistance: The property of a component to oppose the flow of electrical current through itself.

Capacitance

Capacitance: The property of a component to oppose any change in voltage across its terminals, by storing and releasing energy in an internal electric field (John, 1993, 52-63).

Inductance

Inductance: The property of a component to oppose any change in current through itself, by storing and releasing energy in a magnetic field surrounding itself.

Constructed and the Ways in Which They Are Less Than Ideal

In this paper, we will examine each type of component. We will see how they are made and what basic properties they have (Chang, 2008, 2124). Then we will see how they behave when a fixed, dc voltage is applied to them, both by themselves and in combination with other types of components (Kyeon, 2008, 1105). Once we see how they behave in response to dc voltages, another set of pages will explore how these components respond to the application of ac voltages.

Circuit Components: the Resistor

The resistor is the simplest, most basic electronic component. In an electronic circuit, the resistor opposes the flow of electrical current through itself. It accomplishes this by absorbing some of the electrical energy applied to it, and then dissipating that energy as heat. By doing this, the resistor provides a means of limiting or controlling the amount of electrical current that can pass through a given circuit (Park, 2007, 755).

Resistors, such as the two pictured to the right, have two ratings, or values, associated with them. First, of course is the resistance value itself. This is measured in units called ohms and symbolized by the Greek letter Omega (Brandao, 2007, 951). The second rating is the amount of power the resistor can dissipate as heat without itself overheating and burning up. Typical power ratings for modern resistors in most applications are ½ watt and ¼ watt, which are the two sizes shown in the figure. High-power applications can require high-power resistors of 1, 2, 5, or 10 watts, or even higher.

For purposes of physical comparison, the larger resistor to the right is rated at ½ watt; its body is a cylinder 3/8" long and 1/8" in diameter (Charles, 2004, 92-113). The smaller resistor, rated at ¼ watt, is of the same shape but is only 1/4" long and 1/16" in diameter.

The length and diameter of the cylinder are controlled in order to define the resistance value of the resistor — the longer the cylinder, the greater the resistance; the greater the diameter, the less the resistance. At the same time, the larger the cylinder, the more power it can dissipate as heat (Richard, 1997, 33-41). Thus, the combination of the two determines both the final resistance and the power rating.

A newer, more precise method is shown to the left. The manufacturer coats a cylindrical ceramic core with a uniform layer of resistance material, with a ring or cap of conducting material over each end. Instead of varying the thickness or length of the resistance material along the ...