Inductors are passive electronic components that are used alongside capacitors and resistors to form complex and simple circuits. Inductors are just metalic conductor usually insulated copper coil wound on a soft iron or ferrite core to Increase the efficiency and inductance.
They store electricity in form of magnetic field. Inductors are use in radio tunning and AC circuits, voltage filters etc. Working principles of an inductor. When electric current passes through an inductor, magnetic field is produced around it, the magnetic field produced is converted back to current which then flows backwards when the supplied current is removed or flunctuating. Inductors tends to oppose fluntacting or uneven change in current due to the current stored in it in form of magnetic field, this characteristics is applied in current regulation. Inductors allows DC to pass through them but blocks AC from passing through because of it flunctuating nature, when an inductor is specifically designed for blocking AC it is called a choke. According to Lenz's law, the induced voltage has a polarity(direction) which opposes the change in current that creates it. As a result inductors stops any changes in current through them and this resistance is called inductive reactance. The ability of an inductor to store current in form of magnetic field is known as inductance measured in Henry(H) named after the 19th century American scientist, Joseph Henry.
Types of Inductors.
Inductors are classified according to their sizes, advantages of the types of materials use to make them and their appllications.
There are two types of inductors;
Fixed inductors: their inductance value can be increased or reduced.
Variable inductors: their inductance can't be varied i.e their inductance is always fixed.
1. Air core Inductors.
Air core inductors are coreless, they might be wound on plastics, foam, ceramics or other insulators.Coreless inductors are very efficient than other types because there is no core or iron losses as observed in iron core inductors. They are usually use in radio circuits, audio circuits, tunning systems and also connected along with integrated circuits to filter radio signals.
2. Vairable Inductors.
They have a variable Inductance, Their inductance can be varied by tunning the ferrite core in a screw thread.
3. Iron core Inductors.
Their core is made of insulated soft iron sheet or laminated iron block. They suffer from eddy current and core loses therefore, this reduces efficiency.
4. Torroidal Inductors.
This inductors is usually in form of a donut shape. It is made by wounding insulated copper wire on a ferrite bead. Torodial inductors are in commonly used PCBs and also in modern flourencent bulbs.
4. RF Inductors.
Rf inductors are radio frequency inductors use at high resonant frequencies. It is characteristised by low current rating and high electrical resistance. But as high frequencies are used the coil resistance increases. The are used along with capacitors in generating and receiving high frequency radio wave for communication and wireless power transfer.
5. Powdered iron core Inductors.
Their core is made of laminated iron shits separated by powdered materials to reduce email current loss. they are efficient because they have minimum core losses.
6. Ferrite core Inductors.
Their core is made of ferrite, it comes in different sizes and shapes. They are use in power bank circuits, PCBs and micro electronics.
Circuit applications of Inductors.
1. Freqency tunning. 
An inductor is coupled with a variable capacitor in parallel to make a tunning circuit which is use to tune to different radio frequencies depending on the frequency of the tunned circuit.
2. Filtering and decoupling.
Inductors are use for regulating and filtering current from hums and flunctuation. Current regulation. They're use for regulating current by connecting it in a circuit along + lines polarity.
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Basic Electronics