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,
i = lim
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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