= Quasistatic electromagnetic approximation
A <quasistatic electromagnetic approximation> neglects propagation delay over a vacuum device of characteristic size $L$ when $\omega L/c\ll1$. It does not automatically discard every time <derivative>: an <Ampere-Maxwell law> calculation in a capacitor gap must retain <displacement current>. In a medium use the relevant propagation and response scales. The dominant approximately static <electric field> can be used to calculate a smaller induced <magnetic field>, provided the corrections to the dominant field remain small. Near a resonance or for a large distributed circuit, the size criterion alone may not justify an instantaneous lumped model.
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