The concentration of donor impurity atoms in silicon is $N_{d}=10^{15} \mathrm{~cm}^{-3}$. Assume an electron mobility of $\mu_{n}=1300 \mathrm{~cm}^{2} / \mathrm{V}-\mathrm{s}$ and a hole mobility of $\mu_{p}=450 \mathrm{~cm}^{2} / \mathrm{V}-\mathrm{s}$.
(a) Calculate the resistivity of the material.
( $b$ ) What is the conductivity of the material?