= Magnetic field between circular capacitor plates
{title2=$\widetilde B_\phi(s)=-i\omega\mu_0\epsilon_0V_0s/(2d)$}
For a circular air-filled <parallel-plate capacitor> with voltage phasor $V_0e^{-i\omega t}$, uniform gap $d$ and radius $a$, the <Ampère-Maxwell equation> on a circular loop of radius $s<a$ gives the displayed <magnetic field>. The enclosed <displacement current> is proportional to $s^2$, whereas the circulation is $2\pi sB_\phi$. Consequently its amplitude grows linearly from zero on the axis. This assumes negligible <fringing fields> and a <quasistatic approximation> $\omega a/c\ll1$.
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