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An inductor is a passive component built to store energy within its magnetic field by coiling a wire around a magnetic core. When current flows through an inductor, the voltage across it is directly proportional to the rate of change of the current over time. This relationship is expressed mathematically using inductance, measured in henry, which represents the inductor's ability to resist changes in current flow.

An inductor's inductance is determined by its physical dimensions, core material, and construction method. The size and shape of the coil, combined with whether the core is made from iron, steel, plastic, or air, all influence the inductance value. These design factors allow inductors to range from a few microhenrys in communication systems to tens of henrys in power systems.

Inductance opposes abrupt changes in current flow, a property called inductance resistance. When voltage is applied across an inductor, the current cannot change instantaneously because the inductor generates a counter-voltage proportional to the rate of current change. This characteristic makes inductors essential for controlling current transitions in circuits and protecting components from sudden current spikes.

A linear inductor maintains constant inductance regardless of current flow, producing a straight-line voltage-current relationship. A nonlinear inductor's inductance varies with the current, resulting in a curved voltage-current plot. Linear inductors are more predictable in circuit design, while nonlinear inductors exhibit changing inductance values as operating conditions vary.

Inductors are commonly referred to as coils or chokes in electrical engineering. These alternative names reflect their construction as wound wire coils and their function of choking or restricting changes in current flow. All three terms—inductor, coil, and choke—describe the same passive component used to store magnetic energy.

Fixed inductors have a constant inductance value determined by their construction and are used when a specific inductance is required. Variable inductors allow adjustment of inductance by changing the core position or configuration, providing flexibility in circuit tuning and optimization. Both types are commercially available with inductance values suited to specific applications, from microhenrys to tens of henrys.

Inductance is the constant of proportionality in the relationship where voltage across an inductor equals inductance multiplied by the rate of change of current over time. This mathematical expression, expressed using the passive sign convention, defines how inductors respond to changing currents. Understanding this relationship is fundamental to analyzing inductor behavior in circuits and designing systems like the automobile ignition system.