[[Electric Force, Field, and Potential]]
# Summary
* Electric field at a point = electric force on a positive test charge divided by charge = $\vec E=\frac{\vec F_E}{q}$ (unit N/C).
* Test charge's impact on field is negligible.
* Field lines point towards negative and away from positive. Closer lines = stronger field.
* Net field from several charges is sum of vectors.
* Inside a conductor in electrostatic equilibrium field is zero. Charge sits on surface, surface field is perpendicular to surface.
* Inside a charged insulator inside can be nonzero since charge stays instead of moving to surface.