voltage is a measure of difference in electric potential energy across two points
\begin{equation} V = \frac{1}{4\pi \epsilon_{0}} \sum_{i} \frac{q_{i}}{r_{i}} \end{equation}
or,
\begin{equation} PE = qV \end{equation}
potential energy experienced by \(q\) at the point.
\begin{equation} E_{x} = -\dv{V}{x} \end{equation}
\begin{equation} \Delta V = - \int E \cdot dr \end{equation}
\begin{equation} PE = \frac{1}{4\pi \epsilon_{0}} \frac{q_1q_2}{r} \end{equation}
equipotentential lines and electric field lines should align at right angles.
- current through series is the same
- voltage through parallel is the same