HomeElectrical EngineeringInductors: Types, Specifications, Working and Application of Inductors

Inductors: Types, Specifications, Working and Application of Inductors

In this post, you’ll learn what is inductors it’s types, working, specification, factors, colour coding and application of inductors.

Inductors and Types

Inductors is an electrical/electronic component that opposes a change in current due to its self-inductance. It consists of a number of turns of fine wire of copper wound on a core of some material (air, iron, powdered iron or ferrite material) in spiral form.

When the current flows through a coil of inductor it induces EMF due to the effect of electromagnetic induction which opposes the change in the cause for it (applied current).

Inductors and types

Specification of Inductors

The specifications of inductors are:

  1. Inductance value
  2. Resistance
  3. Capacitance
  4. Frequency range
  5. Quality factor
  6. Power loss
  7. Current rating
  8. Temperature coefficient

1) Inductance value:

The value of inductance is measured in terms of its inductance value and is expressed in henries, millihenries and microhenries.

2) Resistance:

Resistance is the ohmic value of an inductor wire, which is expressed in ohms.

3) Capacitance:

Stray capacitance effect exists in an inductor, i.e. a coil has some capacitance between windings which is called as stray capacitance. It lies between 1 to 10pF.

4) Frequency range:

The frequency range is the maximum frequency up to which the inductor can work safely.

5) Quality factor:

Reciprocal of the power factor is the quality factor. It is the ratio of inductive reactance (XL) to the resistance (R) of the coil. It is merely a number. For good coil, Q must be high and R must be low.

i.e. Q-factor=XL/R

6) Power loss:

The loss in the coil is due to the copper wire, stray capacitance and resistance of the coil. Less the power loss greater will be the quality of the coil.

7) Current rating:

Current rating is the operating current of an inductor and it is measured in Amps.

8) Temperature coefficient:

The temperature coefficient represents the stability in inductance value with change in temperature. It is expressed in ppm/°c.

Read also: Types of circuits, Kirchhoff’s Law and Its Classification

Factor Influencing the Inductance of an Inductor

The inductance of an inductor is,

  • Is directly proportional to the square of the number of turns (N2) of the coil.
  • Directly proportional the area (A) enclosed by each turn.
  • Directly proportional to the permeability of the core (µa).
  • Inversely proportional to the length (l) of the coil.


  • µa = Absolute Permeability of the core material
  • µo = Absolute Permeability of air
    • = 4π(Pi)x10^-7 H/m
  • µr = Relative permeability of the core material

Types of Inductors

Inductors are mainly classified depending on the core material used and operating frequency.

Following are the different types of inductors:

  1. Iron Cored Inductors
  2. Air Cored Inductors
  3. Powdered Iron Cored Inductors
  4. Ferrite Cored Inductors
  5. Variable Inductors
  6. Audio Frequency Inductors
  7. Radio Frequency Inductors

1) Iron Cored Inductors

Iron Cored Inductor symbol
  • The figure represents the constructional details and symbol of an iron cored inductor which consists of a coil wound on laminated iron core or cobalt or nickel alloys.
Iron Cored Inductor
  • Two lead are connected to two ends of the coil and is also centre tapped to the half of the length of the coil.
  • It is also known as a transformer that consists of primary and secondary windings in which two leads are soldered to primary and three

Applications: These are used:

  • At low power frequency (50Hz) for building surge voltages.
  • At audio frequency (20Hz – 20kHz) as AF chokes for tone control.
  • As filter chokes with the capacitor in power supplies.

2) Air Cored Inductors

Air Cored Inductor symbol
  • The figure represents the constructional details of air-cored inductors which consist of air as core material, i.e. coil is wound on an insulating Bobin that contains air.
Air Cored Inductors
  • These can be operated at radio frequencies.

Applications: These are used:

  • As RF chokes, RF transformers andIF transformers

3) Powdered Iron Cored Inductors

Powdered Iron Cored Inductor symbol
  • Constructional details of the powdered iron cored inductor are shown in the figure, in which powdered iron rods are used as cores.
  • These are used at higher frequencies.
Powdered Iron Cored Inductor

Applications: These are used:

  • RF chokes, RF transformers in radio receivers.
  • As IF transformers and IF chokes in radio receivers.
  • As an arial coil in tuned circuits of radio receivers.
  • For tuning radio connected with gang condensers.

4) Ferrite Cored Inductors

  • Ferrite cored inductors contain coils wound on a solid core made of ferrite material. These are pot core and toroidal core type inductors as shown in the figure.
Ferrite Cored Inductors

Applications: These are used at higher frequency ranges.

  • For radio interference suppression.
  • As filter chokes.
  • For colour T.V. raster generation.

5) Variable Inductors

  • The inductors whose inductance value can be varied continuously are known as variable inductors. The constructional details are shown in the figure.
Variable Inductors
  • Here threaded screw is used as screw, which can be rotated in or out of coil to vary the inductance value.

Applications: These are used,

  • Tuning circuits
  • Coupling circuits
  • Oscillator circuits
  • Timing circuits

6) Audio Frequency (A.F.) Inductors (AF Chokes)

Audio Frequency Inductors symbol
  • Choke is an inductor that opposes a change in current. If choke operates at audio frequency range then it is called as A.F. choke or A.F. inductor.
Audio Frequency Inductors
  • It contains a number of turns of thin wire wound on a laminated iron core as shown in the figure.
Audio Frequency Inductor
  • The wire is made up of insulated copper and the unit is placed in a metal casing.

Applications: AF chokes are used,

  • As filter chokes in radio and T.V. receivers.
  • For generating voltage surges in fluorescent lamp sets.
  • In tube light sets.

7) Radio Frequency (R.F.) Inductors (R.F. Chokes)

Radio Frequency Inductor
  • These are designed to operate at radio frequency range (>20 kHz), shown in the figure.
Radio Frequency Inductor
  • They consist of a number of turns of thin wire wound on an insulator tube or powdered iron core. For higher permeability, powdered iron cored is used.

Applications: These are used:

  • Inductors are used.
  • In radio transmitters.

Inductance Colour Coding

According to the EIA standard, the colour code table for the inductor is given below. To identify the value of inductor the following steps are used:

  • Hold the inductor so that colour bands should start from the left-hand side.
  • Read the bands from left to right.
  • The first band indicates the first digit, the second band indicates the second digit, the third band indicates the multiplier or number of zeroes to be added after the second digit and the fourth band indicates the tolerance in percentage.
Inductance Colour Coding chart

Applications of Inductors

Inductors are used:

  • Communication circuits
  • Filter circuits
  • Tuning circuits
  • Magnetic amplifiers
  • Fluorescent lamps
  • Telemetric equipment
  • Modulating and demodulation circuits
  • Radar sets.

That’s it, thanks for reading. If you have any questions about “inductors and its types” you can ask in the comments. Share this article if it is worth sharing.

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Saif M
Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at theengineerspost.com