It is known by **self-induction** to the phenomenon of electromagnetic origin that occurs in physical systems, for example in electrical circuits, leading to the formation of induced currents in the circuit, which is produced by the variation of the flow of the initial current.

We call an **inductor** a circuit that is made up of a conductor that is wound around the core. Therefore when the inducing element and the induced element are the same, then self-induction appears.

Let’s see the components of this process:

When in a **solenoid** like the one in the image of **N** turns with a length **l** and a section **S** , which is traversed by a current whose intensity we denote by **i** , then:

1. The **magnetic field** produced by the current that runs through our solenoid is uniform and parallel to its axis. The value of the magnetic field is calculated by applying Ampère’s law: where μo is the permeability of the vacuum. 2. The magnetic field just mentioned crosses through the turns of our solenoid; the flow of the mentioned field through all the turns of the solenoid is known as **eigen flux** , and is calculated by the following expression: 3. We call the **coefficient of eigen** flux (ϕ) and the intensity (i) the **self-induction coefficient** ; it is denoted by **L: L = ϕ / i** .

The self-induction coefficient depends solely on the geometry of our circuit and the magnetic properties of the solenoid that we have placed inside the circuit. Self-induction will be greater if the core of our solenoid is iron.

The unit of measurement used to measure self-induction is called henry (H).

4. According to Faraday’s electromagnetic induction law, if the intensity of the current changes over time, an **eloctromotor force** ( **fem** .) Is generated in the circuit (it would be the red arrow that we can see in the image) , which is opposed to changes in flow. The **self-induced emf** that we denote by **VL**

it is obtained by deriving the expression of the eigenflow with respect to time. This force always acts in the sense that it opposes the variation of the current.

In order to help us understand this phenomenon, we can think of one of the easiest examples to see that was discovered by Faraday in 1831. Michael Faraday discovered that if you *wind a magnet in a spiral of wire* , an electric current can be generated in the magnet. . This current is known as a coil or solenoid (which we have mentioned so much throughout the article). When the magnet moves inside the solenoid, a current is induced, which produces a voltage. The magnitude of the induced voltage will depend on the turns around the nucleus, that is, on the number of turns of the inductor.