Copper has one conduction electron per atom, a density of 9 and an atomic weight of 64 . Show that $n_{0}$, the number of free electrons per unit volume is $\approx 8 \times 10^{28} \mathrm{~m}^{-3}$ and that the value of its Fermi energy level is about $7 \mathrm{eV}\left(1 \mathrm{eV}=1.6 \times 10^{-19} \mathrm{~J}\right)$.