Sunday, September 16, 2012

Working of Inductors

What is an inductor?

  • An inductor is merely, a wire wound to form a coil. It is a passive two

terminal device or electrical component which has the capability to store energy in magnetic field.

Varying the current flowing in the inductor with time produces or induces a voltage in the coil in accordance with the faraday’s law of electromagnetic induction which states that an EMF proportional to the rate of change of magnetic flux is induced in the coil or the closed circuit . This voltage according to the Lenz’s Law opposes the change in current which created it.

Inductors are the basic electrical components used in electric circuits which require the value of the current and voltage flowing through it to be changed with time. Inductors possess properties to delay and reshape the alternating current.

How an inductor works?
Let us consider a circuit with a battery , a switch ,  a light bulb , a coil of wire wound around a piece of Iron . The coil of wire used here is an inductor with an Iron core.  Now if we take this circuit without the inductor, the bulb lights up normally but if the inductor is taken into consideration the behavior of the circuit is totally different.

The light bulb acts as a resistor .The wire used here has a low resistance and one can expect that the current shall follow the low resistance path and bulb will be very dimly lit up. But what happens is that when we close the switch the bulb burns brightly and gets dimmer. When the switch is open the bulb lights up brightly and turns off quickly.
This happens due to the presence of inductor.

When current flows into the coil, a magnetic field is set up. While this field is developing, the coil stops the flow of current and allows the current to flow once the field is setup. When we open the switch, magnetic field present keeps the current flowing in the circuit and this current goes off as the magnetic field in this coil collapses.
This shows the fact that the inductor stores energy in the magnetic field and the inductors resist any change in the value of current flowing through it.


  • HenryStandard unit of inductance is Henry.  Named after a scientist Joseph Henry who discovered electromagnetic induction with Faraday.

Capacity of an inductor depends upon the following four factors

  • Number of coils – More the number of coils more is the inductance.

  • The Material around which the coil is wrapped (core)

  • Cross Sectional Area of the coil - Larger the area, more the inductance.

  • Length of the coil –smaller the coil, more the inductance as smaller coil means narrower coils.The formula for calculating the capacity of an inductor is given by
    H= 4π X number of turns X area of coil X mu / coil lengthwhere mu is permeability of core. Permeability of air is 1 while that of steel is 2000. 

  • Applications Of Inductors

  • Used extensively in analog circuits and processing of the signal.

  • Along with capacitors in many tuning circuits.

  • Used in transformers to have coupled magnetic flux from two or more inductors.

  • In switch mode power supplies, inductors are used to store energy.

  •   In electrical transmission systems to reduce the voltage from lightning strikes and to limit switching as well as fault currents.


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