The coil is wound around an insulating tube by a wire, and the wires are insulated from each other. The insulating tube can be hollow, or it can contain an iron core or a magnetic powder core. The inductance of the coil is represented by L, and the units are Henry (H), millihenry (mH), microhenry (¦ÌH), 1H=10^3mH=10^6¦ÌH.
