hardware//electronics//component//inductor

An inductor is an electronic component made of a coil of wire that stores energy in its magnetic field and resists changes in the current through it, and it is used to smooth currents in power supplies, to filter signals, and, as an electromagnet, to make strong fields on demand. A **solenoid** is the long, straight version, and a coil around an iron core is an electromagnet.

An inductor is an electronic component made of a coil of wire that stores energy in its magnetic field and resists changes in the current through it, and it is used to smooth currents in power supplies, to filter signals, and, as an electromagnet, to make strong fields on demand. A solenoid is the long, straight version, and a coil around an iron core is an electromagnet.

Coiling the wire is what makes it work. A single straight wire makes a weak field that circles it; wound into a coil, each turn adds its field to the others along the axis, so inside a long solenoid the field is nearly uniform and grows with the number of turns per metre and with the current, B=μ0nIB = \mu_0 n IB=μ0​nI. Near the ends, and in a short coil, the turns far away contribute less, because each turn's field weakens with distance, so a short fat coil is less uniform and less efficient than a long one.

An inductor fights changes in its own current.

Because a changing current changes the coil's own flux, the coil induces a voltage against the change: it slows a current's rise, and when the current is cut it pushes back hard, which is why switching off an inductive load can spark.

That opposition is measured as inductance, in henries: one henry induces one volt when the current changes by one ampere per second.

The same coil, driven with a fast pulse of current, becomes the business end of a transformer or of a magnetic stimulator (transcranial magnetic stimulation in Lobeworks/17).

An iron core multiplies the field many times, because the iron's own magnetic domains line up with it; that is how electromagnets in relays, motors and scrapyard cranes get their strength.