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Symbols of Inductors

Introduction to Inductor

  • The Inductor is one of the passive electrical component which is just a coil of wire that is designed to induce a magnetic field in itself or in the core when a current is flowing through the coil. It is also called as a "Choke".

  • Inductors have the exact opposite characteristics of capacitors i.e. capacitors store energy in the form of an electric field (produced by the voltage between two plates), inductors store energy in the form of a magnetic field (produced by the current through wire).

  • As the stored energy in a capacitor tries to maintain a constant voltage across its terminals, similarly, the stored energy in an inductor tries to maintain a constant current across its windings.

  • Because of this property, inductors opposes the change in current. This property makes inductors in filter circuits benefits power supplies.

  • Higher the inductance, longer time is taken by a given voltage to produce a given current.

  • The unit of inductance is Henry and inductor can be measured through LCR meter.

  • Inductors are also known as AC resistor. A fully discharged inductor having zero current through it will initially act as an open circuit when attached to a source of voltage in a circuit.

  • Construction of Inductor

    Symbols of Inductors

    Important Concepts:

    Lenz's Law
  • Lenz's Law says that in a circuit with an induced EMF caused by a change in a magnetic field, the induced EMF causes a current to flow in the direction that opposes the change in flux. In other words, if an increasing magnetic field induces an EMF(Electro-Motive Force), the resulting current will oppose a further increase.

  • When a current through inductor is increasing due to positive induced voltage, it is said to be charging. similarly, current through inductor is decreasing when voltage induced becomes negative at the terminal where current entered positively, then it is said to be discharging as the energy from magnetic field is returned back to source.

  • Mutual Inductance of an Inductor
  • Mutual Inductance is a property of inductor when two or more inductors are connected in closeness having their magnetic flux coupled

  • The mutual inductance depends on the relative positioning of two coils. i.e. when two coils are placed next to each other at a small distance then mutual inductance of larger value is produced. Similarly, when two coils are placed apart or at different angle then the value of mutual inductance produced will be small.

  • Magnetic field due to two coils:
    Magnetic field due to two Coils of Inductor

    Magnetic field due to two Coils of Inductor

    Classification of Inductors


    Air Core Inductor

  • It is a fixed type inductor which has small inductance and commonly used in RF(Radio frequency) applications.

  • The name itself says that air is the core of this inductor due to which there is low losses resulting high Q-factor.

  • It can operate at high frequency ranging up to 1GHz.

  • Stray field radiation and pickups occurs due to electromagnetic interference which becomes substantial with increase in the diameter of the coil.
  • Air Core Inductor

    Iron Core Inductor

  • It is a fixed type inductor and used in high power and high inductance value

  • These inductors are limited in high frequency due to hysteresis of capacitor.

  • They are widely used in Audio Equipment, industrial power supplies, inverter systems etc.

  • The core assist in increasing the inductance without increasing the number of turns

  • Iron Core Inductor

    Tapped Inductor

  • It is a type of variable inductor.

  • It consists of a coil having large number of turns and wound on a magnetic core with a desired number of tappings.

  • Where Tap is a conducting wire taken out from coil at a desired distance due to which different mutual inductance can be achieved over the same inductor.

  • Tapped Inductor

    Inductors in Series and Parallel:

    Inductor in series: L(total) = L1 + L2 + L3

    Inductor in parallel: 1/L(total) = 1/L1 + 1/L2 + 1/L3

    Losses in Inductors

  • Loss is a factor which degrades the performance of an Inductor.

  • The various losses in inductor are:
    1. Copper loss: In Copper loss, there is a power loss in terms of heat by the flow of current through winding.

    2. Core loss: It is caused by an alternating magnetic field in core of inductor. It is function of operatig frequency and total magnetic flux swing.

    3. Eddy current: This loss is due to a magnetic core material having an electrical conductivity.

    4. Skin Effect: There is a loss because of skin effect as the alternating current flows through the surface of a conductor.


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