# Thus i 24 b figure 22 a short circuit r

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Unformatted text preview: rcuit is usually a connecting wire assumed to be a perfect conductor. Thus, | i (2.4) (b) Figure 2.2 (a) Short circuit (R = 0), (b) Open circuit (R = ∞). Problem Solving Workbook Contents 30 PART 1 DC Circuits A short circuit is a circuit element with resistance approaching zero. Similarly, an element with R = ∞ is known as an open circuit, as shown in Fig. 2.2(b). For an open circuit, v i = lim =0 (2.6) R →∞ R indicating that the current is zero though the voltage could be anything. Thus, (a) An open circuit is a circuit element with resistance approaching inﬁnity. (b) Figure 2.3 Fixed resistors: (a) wirewound type, (b) carbon ﬁlm type. (Courtesy of Tech America.) (a) (b) Figure 2.4 Circuit symbol for: (a) a variable resistor in general, (b) a potentiometer. A resistor is either ﬁxed or variable. Most resistors are of the ﬁxed type, meaning their resistance remains constant. The two common types of ﬁxed resistors (wirewound and composition) are shown in Fig. 2.3. The composition resistors are used when large resistance is needed. The circuit symbol in Fig. 2.1(b) is for a ﬁxed resistor. Variable resistors have adjustable resistance. The symbol for a variable resistor is shown in Fig. 2.4(a). A common variable resistor is known as a potentiometer or pot for short, with the symbol shown in Fig. 2.4(b). The pot is a three-terminal element with a sliding contact or wiper. By sliding the wiper, the resistances between the wiper terminal and the ﬁxed terminals vary. Like ﬁxed resistors, variable resistors can either be of wirewound or composition type, as shown in Fig. 2.5. Although resistors like those in Figs. 2.3 and 2.5 are used in circuit designs, today most circuit components including resistors are either surface mounted or integrated, as typically shown in Fig. 2.6. (a) Figure 2.5 | v v Figure 2.6 Resistors in a thick-ﬁlm circuit. (Source: G. Daryanani, Principles of Active Network Synthesis and Design [New York: John Wiley, 1976], p. 461c.) |...
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