Formula Info
\begin{aligned}F&=k\frac{|q_1q_2|}{r^2}\\E&=k\frac{|q|}{r^2}\\\vec E_i&=kq_i\frac{\vec r-\vec r_i}{|\vec r-\vec r_i|^3}\\\vec E_{total}&=\sum_i\vec E_i\\\vec F_{test}&=q_{test}\vec E_{total}\end{aligned}
k = 8.9875517923 × 10⁹ N·m²/C². Charges are entered in µC and converted to C; coordinates are meters and fields are N/C.
Positive charges point outward; negative charges point inward. Contributions add as vectors. A negative test charge feels force opposite the field and does not alter the source field.
Ideal point charges in vacuum. Nonzero charge locations and distances below 1 µm are undefined; no clipped field is reported. A zero field has no direction.
