However, all physical devices are connected to a circuit through conductive leads and paths, which contain inherent, usually unwanted, inductance.
[2] An easy way to deal with these inherent inductances in circuit analysis is by using a lumped element model to express each physical component as a combination of an ideal component and a small inductor in series, the inductor having a value equal to the inductance present in the non-ideal, physical device.
Ideally, the impedance of a capacitor falls with increasing frequency at 20 dB/decade.
However, due partly to the inductive properties of the connections, and partly to non-ideal characteristics of the capacitor material, real capacitors also have inductive properties whose impedance rises with frequency at 20 dB/decade.
At the resonance frequency the sum of both is minimal, above it the parasitic series inductance of the capacitor dominates.