Houjun Liu


current is defined as the flow of positive charge. Specifically:

\begin{equation} I = \frac{\Delta Q}{\Delta t} \end{equation}

resistance of a wire

(if ever you come across needing to calculate the resistance of the wire from scratch)

\begin{equation} R = \rho \frac{L}{A} \end{equation}

where, \(\rho\) is the material resistivity, \(L\) the length, and \(A\) the cross-sectional area.

you rarely need to do this!