Explain the classification of materials on the basis of resistivity.

(N/A) Materials are classified into three categories based on their resistivity: conductors,semiconductors,and insulators.
$1$. Conductors: For a perfect conductor,the resistivity is $0 \ \Omega m$ and conductivity is infinite. For metals,the resistivity typically ranges from $10^{-8} \ \Omega m$ to $10^{-6} \ \Omega m$.
$2$. Insulators: For a perfect insulator,the resistivity is infinite and conductivity is $0$. For materials like ceramic,rubber,and plastic,the resistivity is about $10^{18}$ times higher than that of metals.
$3$. Semiconductors: The resistivity of semiconductors lies between that of metals and insulators. $A$ key characteristic is that the resistivity of semiconductors decreases with an increase in temperature.