What is an Inductor?

An inductor, also called a coil, choke, or reactor is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a coil.

Inductors are commonly seen in electromagnets, heating elements, and motors and generators.

To see what an Inductor looks like as a Schematic Symbol, check out our page on Schematics.

Faraday's Law of Induction

Faraday's law is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF) a phenomenon known as electromagnetic induction. It is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators, and solenoids. In plain terms, this means that magnetic fields will induce magnetic fields on other inductors. The intensity of the magnetic field due to current flow, number of coils, and distance from each other will have a direct and predictable relationship between the two inductors. 

In the image to the left, the voltage from the inductor on the right will induce a volage 3 times smaller on the inductor on the left- this is because there are three times fewer wraps of the coil from the right to left. 

Electromotive Force: Lorentz Law

The magnetic force component of the Lorentz force is responsible for motional electromotive force, or motional EMF, which is the underlying phenomenon in many electrical generators. When a conductor is moved through a magnetic field, the magnetic field exerts opposite forces on electrons and nuclei in the wire, and this creates the EMF. The term "motional EMF" is applied to this phenomenon since the EMF is due to the motion of the wire. In other words, if you pass a current through a generator it will act as a motor and spin. However, if you spin a generator, it will produce a current. In the case where you spin the generator, the voltage created is the same force created in any other voltage source. When wired in a way that is working with anticipated current, this creates usable power. In contrast, when voltage is applied to an inductor, transforms that voltage into motion, heat, or a magnetic field, and any voltage that is not transformed into another type of energy will exhibit as an electromotive force opposing current flow.  

If we remember from our page on resistance, resistance is defined as an opposition to current flow- so in this way, an inductor will have a small "resistance" on a circuit as Electromotive Force. We can find the direction of this force using the Right-Hand Rule. If you hold your right hand up, where your pointer finger is pointing in the direction of the magnetic field,  your thumb is pointing in the direction of current flow, your middle finger bent at 90 degrees will show you the direction of the Electromotive force. 

Lenz's Law

Lenz's Law states that the direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field. It is a qualitative law that specifies the direction of induced current but states nothing about its magnitude. Lenz's law predicts the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or the drag force of eddy currents exerted on moving objects in a magnetic field.

In plain words, a current running through a conductor will induce a magnetic field where likewise a magnetic field on a conductor will induce a current. These currents are called "Eddy Currents."

Common Examples of Inductors


A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit or multiple circuits. A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a conductive connection between the two circuits. Faraday's law of induction describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil.

Transformers are most commonly used for increasing low AC voltages at high current (a step-up transformer) or decreasing high AC voltages at low current (a step-down transformer) in electric power applications, and for coupling the stages of signal-processing circuits. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another. Transformers have become essential for the transmission, distribution, and utilization of alternating current electric power. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid.


Electromagnetism is caused when an electric charge is in motion. When current is flowing through a wire, a small magnetic field is generated. More charges flowing or more coils in the inductor will amplify the electromagnetic field that a wire will produce. 

For more information on Electromagnets and Electromagnetism, check out our page on Magnetism.

Relays and Solenoids

Relays are electronic switches similar to transistors. Unlike transistors though, they are capable of handling high voltages and currents. They also use a magnetic inductor to physically pull switches together or apart instead of having depletion boundaries like transistors. They can be built to be any variety of voltage or current load, or with as many switches for the required need. There are SPDT, DPDT, and many many more. 

For more information on Relays and Solenoids, check out our page on Relays and Solenoids.

Heating Elements

Induction heating is the process of heating electrically conductive materials like metals by electromagnetic induction, through heat transfer passing through an induction coil that creates an electromagnetic field within the coil to melt down steel, copper, brass, graphite, gold, silver, aluminum, and carbide. This happens when the electromagnetic field created physically vibrates the electrons and atoms in a ferrous material. When matter vibrates, it produces heat. 


A choke is a type of inductor, but its application, function, and design differ from other inductor designs. Typically, this electrical component features a donut-shaped core with an insulated coil wrapped around it. As the name implies, a choke cuts off or restricts high-frequency alternating current. It only permits direct current and lower-frequencies alternating current in an electrical circuit to pass through its conductor.

Ferrite Beads

A ferrite bead is a passive device that filters high-frequency noise energy over a broad frequency range. It becomes resistive over its intended frequency range and dissipates the noise energy in the form of heat. Any conductor that processes data will produce EMF as a byproduct of current flowing. A ferrite bead prevents EMF from the conductor it is installed on and limits the exposure from surrounding electronics that produce EMF. You see these often without even noticing on many cables around your house. 

For more information on Inductors and a few experiments to build to further understand them, check out our page on Electronics Projects.