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Every ohmic material has a characteristic resistivity that depends on the properties of Equation 27.11 shows that the resistance of a given cylindrical conductor such as a wire is proportional to its length and inversely proportional to its cross-sectional area. SECTION 27.2 • Resistance 837 ▲ PITFALL PREVENTION 27.5 Resistance and Resistivity Resistivity is property of a sub- Temperature Material Resistivity a (' ( m) Coefficient b ! [(!C) $ 1 ] Silver 1.59 # 10 $ 8 3.8 # 10 $ 3 Copper 1.7 # 10 $ 8 3.9 # 10 $ 3 Gold 2.44 # 10 $ 8 3.4 # 10 $ 3 Aluminum 2.82 # 10 $ 8 3.9 # 10 $ 3 Tungsten 5.6 # 10 $ 8 4.5 # 10 $ 3 Iron 10 # 10 $ 8 5.0 # 10 $ 3 Platinum 11 # 10 $ 8 3.92 # 10 $ 3 Lead 22 # 10 $ 8 3.9 # 10 $ 3 Nichrome c 1.50 # 10 $ 6 0.4 # 10 $ 3 Carbon 3.5 # 10 $ 5 $ 0.5 # 10 $ 3 Germanium 0.46 $ 48 # 10 $ 3 Silicon 640 $ 75 # 10 $ 3 Glass 10 10 to 10 14 Hard rubber &10 13 Sulfur 10 15 Quartz (fused) 75 # 10 16 Resistivities and Temperature Coefficients of Resistivity Table 27.1 a All values at 20°C. b See Section 27.4. c A nickel–chromium alloy commonly used in heating elements. An assortment of resistors used in electrical circuits. Henry Leap and Jim Lehman |