\begin{equation} I = \frac{dQ}{dt} = n \, q \, v_d \, A \end{equation} \begin{equation} \vec{J} = n \, q \, \vec{v}_d \end{equation}
\begin{equation} \rho = \frac{E}{J} \end{equation} \begin{equation} \rho(T) = \rho_0 [1 = \alpha (T - T_0)] \end{equation}
\begin{equation} V = I R \end{equation} \begin{equation} R = \frac{\rho \, L}{A} \end{equation}