Hello
as you know if we add a inductor in a dc circuit such as RL circuit.after the Time constant period (tue) we can assume that inductor is a wire.what about magnetic filed that the inductor produced?why it remains.as we know the magnetic filed remain until we disconnect the power.
read about Faraday's law of induction. Electric current produces a magnetic field. Even with DC. The magnetic field in your case contains energy, which is stored there during the time period. When the initial energy source (voltage or current supply) is cut, the energy in the inductor is released and it will "try to maintain" the current for a period similar to time constant (tue).
It's only considered as a wire for DC-calculations. It's still an inductor for AC and also magnetic field is calculated in a normal way. It's a matter of what you need to calculate. For very high frequency calculations a normal real life inductor often acts like a capacitor. You can only consider it as a wire if you are doing a calculation to find out DC values.
This is a matter of basic physics course. It is Ampere's law, not Faraday's law. But otherwise Slot is right. Ampere's law says that whenever you have current flowing (DC or AC), it is accompanied by vortex magnetic field. In DC case the vortex wouldn't change with time, but it would still be there!