With an increase in temperature,the resistivity of a conductor ........ and the resistivity of a semiconductor ....... .

How does the resistivity of a material depend on temperature? Write the empirical formula.

The length and area of cross-section of a copper wire are respectively $30 \ m$ and $6 \times 10^{-7} \ m^2$. If the resistivity of copper is $1.7 \times 10^{-8} \ \Omega \ m$,then the resistance of the wire is (in $Omega$)

$A$ metal wire of circular cross-section has a resistance $R_{1}$. The wire is now stretched without breaking,so that its length is doubled and the density is assumed to remain the same. If the resistance of the wire now becomes $R_{2}$,then $R_{2}: R_{1}$ is

Space between two concentric conducting spheres of radii $a$ and $b$ $(b > a)$ is filled with a medium of resistivity $\rho$. The resistance between the two spheres will be

The variations of resistivity $\rho$ with absolute temperature $T$ for three different materials $X, Y$ and $Z$ are shown in the graph below. Identify the materials $X, Y$ and $Z$.