Ampere's Circuital Law states that the line integral of magnetic field induction equals the current enclosed times the permeability. ∮→B⋅→dl=μ₀Ienclosed
A capacitor is separated by a region of insulator. During charging/discharging of capacitor, electric current flows in the circuit. However, no actual charge flows in the insulator region of the capacitor. This demands the needs to incorporate a new fictitious displacement current ID in the region which gives rise to a magnetic field in the region.