Explain : .Electrical resistivity is a characteristic property of the

1.	Explain : .Electrical resistivity is a characteristic property of the material..
Answer» Solution :Metals and alloys have very low resistivity in the range of `10^(-8)Omegam" to "10^(-1)Omega m`. A good conductor of electricity has low resistivity and a poor conductor of electricity has a high resistivity. Insulators like rubber and glass have resistivity of the order of `10^12 Omegam " to " 10^(17) Omegam`. Copper and aluminium have very low resistivity (of the order of `10^(-8)Omega m`) due to which they are very good conductors of electricity. [And hence they are GENERALLY USED for electrical transmission lines.] Resistivity of alloys (e.g.. Nichrome, constantan) is higher (of the order of `10^(-6)Omegam`) than those of PURE metals from which they are made. [For this reason, they are commonly used in electrical heating devices like electric iron, toasters, etc.] The resistivity of SEMICONDUCTORS like SILICON (SI) and germanium (Ge) is between those of conductors and insulators and decreases on increasing the temperature. [And hence they are used for making (PN junction) diodes and transistors.]

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