\item $v_{average}=\frac{1}{t_0}\int_{0}^{t_0} v(t) dt
=-\frac{eE}{m}\frac{1}{t_0}[\frac{t^2}{2}]_{0}^{t_0}
=-\frac{eE}{m}\frac{t_0}{2}=:-\frac{eE}{m}\tau$,
- $\qquad t_0=2\tau$
+ $\qquad t_0=2\tau$, $v_{drift}=2v_{average}$
+ \includegraphics[width=12cm]{drude_v.eps}
\item Each of the $n$ electrons per unit volume
transfer the kinetic energy $\frac{1}{2}mv^2_{drift}$
once per $t_0$ to the lattice