Editing Electric field (section)

=== Superposition principle ===
Due to the [[Linear differential equation|linearity]] of [[Maxwell's equations]], electric fields satisfy the [[superposition principle]], which states that the total electric field, at a point, due to a collection of charges is equal to the vector sum of the electric fields at that point due to the individual charges.<ref name="Serway" /> This principle is useful in calculating the field created by multiple point charges. If charges <math>q_1, q_2, \dots, q_n</math> are stationary in space at points <math>\mathbf r_1,\mathbf r_2,\dots,\mathbf r_n</math>, in the absence of currents, the superposition principle says that the resulting field is the sum of fields generated by each particle as described by Coulomb's law:
<math display="block">\begin{align}
\mathbf{E}(\mathbf{r}) = \mathbf{E}_1(\mathbf{r}) + \mathbf{E}_2(\mathbf{r}) + \dots + \mathbf{E}_n(\mathbf{r})  = {1\over4\pi\varepsilon_0} \sum_{i=1}^n q_i {\hat\mathbf r_i\over {|\mathbf r_i|}^2} = {1\over 4\pi\varepsilon_0} \sum_{i=1}^n q_i {\mathbf r_i\over {|\mathbf r_i|}^3}  
\end{align}</math>
where 
* <math>\hat\mathbf r_i</math> is the unit vector in the direction from point <math>\mathbf r_i</math> to point <math>\mathbf r</math>
* <math>\mathbf r_i</math> is the displacement vector from point <math>\mathbf r_i</math> to point <math>\mathbf r</math>.