Resistance and Resistivity
The materials can be classified as conductors, semiconductors and insulators depending on their resistivities, in an increasing order of their values. Metals have low resistivities in the range of `10^(-8)Omegam` to `10^(-6)Omegam`. At the other end are insulators like ceramic, rubber and plastics having resistivities `10^(18)` times greater than metals or more. In between these two are the semiconductors. These however, have resistivities characteristically decreasing with a rise in temperature. The resistivities of semiconductors can be decreased by adding small amount of suitable impurities. This last feature is exploited in use of semiconductors for electronic devices.
Commercially produced resistors for domestic use or in laboratories are of two major types: wire bound resistors and carbon resistors.
The `i- V` graph for material is given at two different temperatures. The correct relation between `T_1 and T_2` is
Options:
(a) `T_1 > T_2`
(b) `T_1 < T_2`
(c) `T_1 = T_2`
(d) `T_1 = 2T_2`