= Uniform-charge estimate at a capacitor corner
{title2=$|E_n|\simeq V/(4d)$}
Four uniform square charge-sheet pairs, rotated around a common corner, contribute equal normal fields there. Their <superposition> is a large central plate pair, so each contributes one quarter of its field. This gives $|E_n|\simeq\sigma/(4\epsilon_0)\simeq V/(4d)$ when the bulk charge-voltage relation is used. It is an approximation for prescribed uniform sheets, not an exact equipotential-conductor result. Reflection in the mid-plane does give zero tangential field for either model.
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