正在加载图片...
186 11.Electrical Properties of Materials SiO, Porcelain Dry wood Fe Doped Si Quartz Rubber Glass Si Ge Mn Ag NaCl Mica GaAs Cu 11 102010-181016101410121010108106101021102.1010 cm Insulators Semiconductors- *-Metals— FIGURE 11.1.Room-temperature conductivity of various materials.(Su- perconductors,having conductivities of many orders of magnitude larger than copper,near 0 K,are not shown.The conductivity of semi- conductors varies substantially with temperature and purity.)It is cus- tomary in engineering to use the centimeter as the unit of length rather than the meter.We follow this practice.The reciprocal of the ohm ( is defined to be 1 siemens(S);see Appendix II.For conducting poly- mers,refer to Figure 11.20. Ohm's Law The resistance (in ohms)can then be calculated by making use of Ohm's law: V=R·I, (11.3) which was empirically found by Georg Simon Ohm (a German physicist)in 1826 relating a large number of experimental ob- servations.Another form of Ohm's law: j=0…8, (11.4) links current density: (11.5) Battery Ampmeter FIGURE 11.2.Schematic representation of an elec- tric circuit to measure the resistance of a conduc- tor. Voltmeter186 11 • Electrical Properties of Materials The resistance (in ohms) can then be calculated by making use of Ohm’s law: V R I, (11.3) which was empirically found by Georg Simon Ohm (a German physicist) in 1826 relating a large number of experimental observations. Another form of Ohm’s law: j , (11.4) links current density: j A I , (11.5) FIGURE 11.1. Room-temperature conductivity of various materials. (Superconductors, having conductivities of many orders of magnitude larger than copper, near 0 K, are not shown. The conductivity of semiconductors varies substantially with temperature and purity.) It is customary in engineering to use the centimeter as the unit of length rather than the meter. We follow this practice. The reciprocal of the ohm (#) is defined to be 1 siemens (S); see Appendix II. For conducting polymers, refer to Figure 11.20. 10–20 10–18 10–16 10–14 10–12 10–10 10–8 10–6 10–4 10–2 1 102 104 106 Quartz Dry wood NaCl Rubber Porcelain SiO2 Mica Glass GaAs Si Ge Doped Si Mn Fe Ag Cu 1 # cm Insulators Semiconductors Metals Battery Ampmeter I e– – + A L V Voltmeter FIGURE 11.2. Schematic representation of an electric circuit to measure the resistance of a conductor. Ohm’s Law