The magnetic field between the plates of a capacitor is given by B = $\frac{\mu_0 I r}{2 \pi R^2}$

r ≥ R r ≤ R r < R r = R

r < R

According to Ampere's law, when r > R, B = $\frac{\mu_0 I_{D r}}{2 \pi R^2}$