Resistance and Resistors

Any device that consumes power has a resistance. A lamp, a vacuum cleaner, and an electric clock all limit current, and therefore have resistances. A resistor also has a resistance, but unlike the appliances listed above, its purpose is to limit current, or establish voltage levels.

In actual practice, most circuits include more than one resistor, as shown in Figure 2.12.

Figure 2.12

When multiple resistors are used in a circuit, they are numbered R1, R2, and so forth on the schematic.

Multiple resistors can be placed in a circuit in two ways: in series or in parallel. Let's briefly examine each type.