Inductors & Inductance Basics

- basic information about inductors and inductance including mutual inductance and self-inductance.

In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field.

Inductors generate an opposing voltage proportional to the rate of change in current in a circuit.

This property also is called self-inductance to discriminate it from mutual inductance, describing the voltage induced in one electrical circuit by the rate of change of the electric current in another circuit.

Inductance is one of the basic circuit parameters used in circuit design and development.

Inductors appear in a variety of formats, as chokes, transformers, inductors and many other items.


Inductance basics

Inductance is caused by the magnetic field generated by electric currents flowing within an electrical circuit. Typically coils of wire are used as a coil increases the coupling of the magnetic field and increases the effect.

There are two ways in which inductance is used:

  • Self-inductance:   Self-inductance is the property of a circuit, often a coil, whereby a change in current causes a change in voltage in that circuit due to the magnetic effect of caused by the current flow.. It can be seen that self-inductance applies to a single circuit - in other words it is an inductance, typically within a single coil. This effect is used in single coils or chokes.
  • Mutual-inductance:   Mutual inductance is an inductive effect where a change in current in one circuit causes a change in voltage across a second circuit as a result of a magnetic field that links both circuits. This effect is used in transformers.

Inductance circuit symbols

The circuit symbol for an inductor indicates the coil nature of the inductor. There are several formats indicating whether the inductor or transformer has a air core or a magnetic core.

Inductor circuit symbols
Selection of inductor circuit symbols

While the basic inductor is widely used in many circuits, the transformer is also used in very many applications.

Transformer circuit symbols
Selection of transformer circuit symbols


Inductance units

When indicating an inductor on a circuit diagram or within an equation, generally the symbol "L" is used. On circuit diagrams, inductors are generally numbered, L1, L2, etc.

The SI unit of inductance is the henry, H. The inductance of a circuit is one henry if the rate of change of current in a circuit is one ampere per second and this results in an electromotive force of one volt.

One henry is equal to 1 Wb/A.


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