Electric field

Planar slice / z = 0

Electric field and potential

The same three-dimensional Coulomb field, sampled on the plane containing all four charges.

Two panels of the four-charge quadrupole: electric field magnitude and directed field lines on the left, signed potential contours on the right.
Positive charges lie at (±1, 0); negative charges lie at (0, ±1). The center is a saddle. Potential vanishes on both diagonals, although the field there is generally nonzero. The excluded source disks are drawing cutoffs.

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