Explain : 'Electrical resistivity is a characteristic property of the material.'
✓
Answer
Metals and alloys have very low resistivity in the range of $10^{-8} \Omega m$ to $10^{-6} \Omega m$. $\rightarrow$ A good conductor of electricity has low resistivity and a poor conductor of electricity has a high resistivity. $\rightarrow$ Insulators like rubber and glass have resistivity of the order of $10^{12} \Omega m$ to $10^{17} \Omega m$. $\rightarrow$ 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.] $\rightarrow$ Resistivity of alloys (e.g., Nichrome, constantan) is higher (of the order of $10^{-6} \Omega m$ ) 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.] $\rightarrow$ 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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