# Knowledge of inductors and component testing

(1) Inductor
The inductor (see Figure 1 and Figure 2) is an electronic component composed of a wire coil. When current passes through the coil, a magnetic field is generated, and the inductor uses the magnetic field to store energy. When the current in the inductor disappears, the magnetic field returns to zero. The ability of an inductor to build a magnetic field is called inductance, and its unit of measurement is Henry (H). The symbol for inductance is L.

①The structure of the inductor
Inductors are usually made by winding a conductor coil on a core material. The core body has two functions: ①It is used to stabilize the wire and provide support for the wire winding; ②Some core body materials can enhance the inductance.

One type of core body is the air core (see Figure 3), which is made of cylindrical cardboard, wood or ceramics, and can be hollow. This type of core is only used to provide coil winding support without affecting the inductance value. Another type of core is made of ferromagnetic materials (such as iron, nickel or ferrite) (see Figure 4). This core material can concentrate the magnetic field and increase the inductance of the inductor.

②Factors affecting inductance
Inductance is a function of the number of turns of the wire, the length of the coil, the cross-sectional area of ​​the coil, and the permeability of the core material. The inductance of a cylindrical inductor can be calculated by the following formula
L=μAN²/l
In the formula, L is the inductance (Henry); μ is the magnetic permeability of the core (H/m); A is the cross-sectional area (㎡) is the length of the core (m), and N is the number of turns of the wire. Magnetic permeability is a measure of how easy it is to generate a magnetic field in a certain material. The greater the permeability of the material, the easier it is to build a magnetic field. Please note that the inductance is proportional to the square of the number of turns of the wire, so the number of turns has a significant effect on the inductance of the inductor.

example 1
Figure 5 shows an inductor with a solid nickel core. The area (A) is 0.25㎡, the length (l) is 0.05m, the number of turns (N) is 5, and the core permeability (μ) is 0.000125 (H/m). Calculate the inductance.
L=μ×A/l×N²=0.000125×0.25/0.05×5²H=0.0156H