Elektrisches Feld

${{\underline {E}}=-}{\underline {\nabla }}\phi -{\color {Gray}{\frac {1}{c}}}{{\partial }_{t}}{\underline {A}}$

einer Punktladung

$E\left({\underline {r}}\right)=\alpha \left(q{\frac {\underline {r}}{\left|{{\underline {r}}^{3}}\right|}}\right)$

mit

$\alpha ={\frac {1}{4\pi {{\varepsilon }_{0}}}}$