The Complete Handbook of Inductors

Chapter 1: Understanding Inductors

What Inductors Are and Why They Matter

An inductor is a passive electrical component that stores energy in a magnetic field. It is made of a coil of wire, usually wound around a core material, and its fundamental job is to resist changes in electrical current. When current through an inductor tries to increase or decrease, the inductor opposes that change by generating a voltage that pushes back. This opposition to current change is called inductance, measured in units called henries (H). A one-henry inductor will produce one volt of opposing voltage when the current through it is changing at a rate of one amp per second.

That simple fact—that inductors resist current change—makes them essential in nearly every power circuit and RF system built today. Without inductors, switching power supplies would not work, electric motors would not start smoothly, radio receivers would pick up noise from every transmitter on the band, and high-frequency circuits would radiate energy uselessly into space. Understanding what inductors actually do, and why they fail, is fundamental to designing, building, and maintaining circuits that perform reliably.

The Physical Reality: How Inductors Store Energy

To understand why inductors matter, it helps to start with a concrete example. Imagine a simple DC circuit with a battery, a switch, a resistor, and an inductor in series. When you close the switch, the battery tries to push current through the circuit. If the inductor were not there, the current would rise instantly to whatever