Inductance is a key parameter in electrical and electronic circuits. Like resistance and capacitance it is a basic electrical measurement that affects all circuits to some degree.
Inductance is used in many areas of electrical and electronic systems and circuits. Components can be in a variety of forms and may be called by a variety of names: coils, inductors, chokes, transformers, . . . Each of these may also have a variety of different variants: with and without cores and the core materials may be of different types.
Understanding inductance and the different forms and formats for inductors and transformers helps provide an understanding of what is happening within the electrical and electronic circuits.
Inductance is the ability of an inductor to store energy and it does this in the magnetic field that is created by the flow of electrical current.
Energy is required to set up the magnetic field and this energy needs to be released when the field falls.
As a result of the magnetic field associated with the current flow, inductors generate an opposing voltage proportional to the rate of change in current in a circuit.
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.
While the basic inductor is widely used in many circuits, the transformer is also used in very many applications.
The advantage of ferrite and iron cores is that they significantly increase the level of inductance and also in the case of a transformer, the coupling between the input and output inductors. They do introduce losses. Air cored inductors and transformers have lower levels of inductance and are often used for RF applications where lower levels of inductance are needed.
Inductance unit definition
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 which can be defined in terms of rate of change of current and voltage.
- Definition of the henry: 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.