Page 203 - The Mechatronics Handbook

0066_Frame_C11 Page 9 Wednesday, January 9, 2002 4:14 PM

TABLE 11.2 Resistance of Copper Wire
AWG Size Number of Strands Diameter per Strand Resistance per 1000 ft (Ω)
24 Solid 0.0201 28.4
24 7 0.0080 28.4
22 Solid 0.0254 18.0
22 7 0.0100 19.0
20 Solid 0.0320 11.3
20 7 0.0126 11.9
18 Solid 0.0403 7.2
18 7 0.0159 7.5
16 Solid 0.0508 4.5
16 19 0.0113 4.7

FIGURE 11.10 The resistance strain gauge.

FIGURE 11.11 The short circuit.

FIGURE 11.12 The open circuit.

Physically, any wire or other metallic conductor will exhibit some resistance, though small. For practical
purposes, however, many elements approximate a short circuit quite accurately under certain conditions.
For example, a large-diameter copper pipe is effectively a short circuit in the context of a residential
electrical power supply, while in a low-power microelectronic circuit (e.g., an FM radio) a short length of
24 gauge wire (refer to Table 11.2 for the resistance of 24 gauge wire) is a more than adequate short circuit.
A circuit element whose resistance approaches infinity is called an open circuit. Intuitively, one would
expect no current to flow through an open circuit, since it offers infinite resistance to any current. In an
open circuit, we would expect to see zero current regardless of the externally applied voltage. Figure 11.12
illustrates this idea.

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