Draw resistivity `rarr` temperature `(rho rarr T)` graph for metals , alloys and semiconductor.

Explanation

`rArr` (a) For metals relation between resistivity and temperature is given by, `rho_(T) = rho_(0)[1 + alpha (T- T_(0))]` hence, relation between `rho_(T)` and T will be straight line.
`rArr` At temperature much lower than `0^(@)` C the graph will be different than straight line and will be as shown in figure below

`rArr` At room temperature graph is a straight line.
(b) Nichrome (alloy of nickel, iron, chromium) bas large resistivity and has weak dependence of resistivity with temperature.

`rArr` Manganin and constantan have similar properties (to resistivity less dependent on temperature) hence they are used in making standard (reference) wire bound resistors.
`rArr` (c) Resistivity of semi conductor decreases with increase in temperature. For semiconductors `rho rarr `T graph will be as shown below.