What is an Inductor and How Does an Inductor Work?

      An inductor is an insulated wire tightly wound around a core. This core can be a ferromagnetic material or plastic or in some cases hollow (air). This relies on the principle of “magnetic flux develops around a current carrying conductor”. If you know about capacitors, you will be familiar with the fact that capacitors store energy by storing equal and opposite charges in its plates. Similarly, inductors store energy in the form of magnetic fields that develop around them. Inductors react differently to AC and DC. But before we delve into “how inductors work”. Let’s look at its construction and features.

1.Construction of an Inductor:

An inductor is very simple to construct with all the other components used in electronics. Here is a guide to making a simple inductor. All you need is an insulated wire and a core material to wind the coil. The core is nothing but a material around which the wire is wound as shown in the above figure. There are different types of inductors depending on the core material used. Some of the common core materials used are iron, ferromagnetic etc. Apart from the type of core material, it also comes in different sizes and shapes including cylindrical, rod, torod and sheet. In contrast to this, there are also inductors that do not have any physical magnetic core. They are called air core inductors or air inductors. The magnetic core plays an important role in changing the inductance of an inductor.

2.How Inductors Work：

Let us start with stating the fact that "magnetic flux will be generated on a current carrying conductor". Similarly, when current passes through an inductor, it generates magnetic flux around it. In other words, the energy applied to the inductor is stored in the form of magnetic flux. The direction of development of the magnetic flux will be opposite to the direction of current flow. Therefore, the inductor can resist sudden changes in the current flowing through it. This ability of an inductor is called inductance and every inductor will have some inductance. This is given by the symbol L and is measured in Henrys.

The inductance of an inductor depends on the shape of the coil, the number of turns wound on the core, the area of the core and the magnetic permeability of the core material. The inductance of an inductor is given by the following formula

L = μN2A / L

L – Inductance of the coil

μ – Permeability of the core material

A – Area of the coil (square meters)

N – Number of turns in the coil

l – Average length of the coil (meters)

3.Inductors in AC circuits:

As mentioned earlier, inductors act differently with AC compared to DC sources. When an AC signal is applied to an inductor, it generates a magnetic field that varies with time because the current that generates the magnetic field itself varies in time. This phenomenon, according to Faraday's law, generates a self-induced voltage across the inductor. This self-induced voltage is denoted by VL. In fact, the voltage generated across the inductor acts in the opposite direction to the current that opposes them. The voltage across the inductor is given by the following formula

V L =L di / dt

VL – Self-induced voltage

di / dt – Change of current with respect to time

If a current of 1 ampere flows through an inductor for 1 second, it will generate 1v across the inductor. Now you can see how the current flowing through an inductor affects the voltage generated across it. The voltage generated is opposite to the current flowing through the inductor.

4.V-I Characteristics of an Inductor:

Let’s refer to the VI characteristic curve of an inductor to better understand the above concepts. When the positive cycle of an AC signal passes through an inductor, the current increases. We know that an inductor hates changes in current, so it will generate an induced voltage to oppose the current causing it. You can observe this in the above figure at 0°, when the current starts to increase, the induced voltage will be maximum. Once the current reaches its maximum, the induced voltage becomes negative in an attempt to prevent the current from decreasing.

This cycle repeats, and from the above figure we can observe that the induced voltage generated in the inductor will act on the changing current flowing through it. Here, the voltage and current are said to be 90° out of phase. Therefore, with an AC signal, the inductor stores and releases energy in the form of a magnetic field in a continuous cycle.

5.Inductors in DC Circuits:

      We now understand how an inductor works with an AC signal source. Let’s see how it reacts when used with a DC signal source. Recall that the formula for the induced voltage across an inductor is given by

V L =L di / dt 

      When a DC signal source is used, the change in current with respect to time will be zero, resulting in a zero induced voltage across the inductor. Simply put, in a DC circuit, an inductor behaves like a simple, ordinary wire with some resistance in its wires. However, there is more to it when using an inductor with a DC signal source in a real circuit. In a real circuit, it takes a short time for the current to go from zero to its maximum value. At this instant, there will be an induced voltage across the inductor that will be a negative maximum value as the current begins to move from zero to its maximum value. Once the current reaches a steady DC state, the induced voltage drops sharply to zero and becomes null. When used with a DC signal source, an inductor will exhibit this short span of induced voltage spikes.

6.Inductive Reactance:

Another important thing to know about inductors is reactance. This is the resistive property that components like capacitors and inductors exhibit to AC electrical signals. The reactance shown by an inductor is called inductive reactance and is given by the formula

XL = 2πFL

From the formula, we can infer that reactance increases as the frequency of the AC signal increases, remember that an inductor hates changing current, so it shows more reactance to high frequency signals. Whereas when the frequency approaches zero or a DC signal is passed through, the reactance becomes zero, just like the conductor through which the input signal is passed.