Electric basics. Article:

Inductance and factors affecting inductance.


Electromagnetic induction.

Is the process of obtaining current in a circuit with the help of magnetic field. Magnetic field is produced by permanent magnets and also by electric current.

Magnetic field is the area around a magnet in which the effect of force produced by a magnet can be detected.

We also need to understand Magnetic flux, it is the pictorial representation of magnetic field in form of lines because magnetic field cannot be seen.

Magnetic flux anables the study of distribution and density of magnetic field. In this article we may use magnetic field and flux interchangeably.

magnetic field

When magnetic field is moved across a conductor, electromotive force is produced in that conductor.

If a conductor form a closed circuit, the induced electromotive force causes an electric current to flow in the circuit, this process is called Electromagnetic induction.

Voltage and Electromotive force mean the same thing, voltage has different names used to representing it depending with where it is being used, we call it electromotive force when we are talking of voltage which cause current to flow in a circuit, usually the source voltage.

    They are Laws of electromagnetic induction which govern the electromotive force induced in a conductor which are:

  1. Voltage is only induced in the conductor when there is a movement of either magnetic field across the conductor or a conductor moved across the field.

    What important is that, they must be a change in flux linkage on the conductor for voltage to be induced in a conductor.
  2. The magnitude (amount) of induced e.m.f is equivalent to the rate of change of the magnetic flux linking the circuit.

When current flow in a conductor, magnetic field is formed along the hole length of a conductor.

The strength of the formed magnetic field can be increased by coiling the conductor into a coil and also depends on the amount of electric current flowing.

The produced magnetic field by current flowing in a conductor or coil also induces voltage in that coil or conductor which act in opposite direction of flow of current responsible for its formation.

This induced voltage is also governed by the laws of electromagnetic induction listed above, that is they must be also a change in flux linkage, in this scenario the changing flux linkage is as a result of current changing in magnitude.

The property of a circuit whereby there is an e.m.f. induced in that circuit by the change of flux linkages produced by a current change is called Inductance.

They are two terms used in inductance which are self inductance and mutual inductance. When the e.m.f. is induced in the same circuit as that in which the current is changing, the property is called self inductance (M) , this is how inductors are designed to offer. (L) self Inductance When the e.m.f. is induced in a circuit by a change of flux due to current changing in an adjacent (nearby) circuit, the property is called mutual inductance (M), this is the basic operating principle of transformers. self Inductance

A device designed with a known value of inductance or made to introduce a known value of inductance into a circuit is called an Inductor. In designing an inductor the factor explained below are taken into account.

NB - ln the following explanations each factor is examined while others factors are kept constant (kept the same).

Factors affecting Inductance.

Number of turns.

number of turns

Inductance varies directly with number of turns, that is if number of turns is increased inductance also increases.

More turns of wire means more field combine to form a strong magnetic field and vice versa since when current pass through a conductor, magnetic field is formed along whole of its length, when this conductor is coiled the field combine to form a strong magnetic field, therefore more turns results in higher inductance.

Cross sectional area of the coil.

cross sectional area

Cross sectional area varies directly with inductance, if cross sectional area is increased, inductance also increase and vice versa.

Large cross sectional area provide a greater space for magnetic field lines paths because field lines never cross each other but they may became distorted, so on large cross sectional area they is more space for magnetic field lines formation. Inductance is high in large cross sectional area.



Inductance varies inversely with length, that is as length increases inductance decreases. This is because a longer path for the magnetic field lines results in more opposition to its formation, so inductance is high on short length.

Core material used.

core material used

The core material provide an easy establishment of magnetic field, Simbol of inductors are based on the core material used such as air. Inductance depends on the core used.

Core material is measured based on permeability, which is the measure of easy with which magnetic field can be formed within a material. Iron core has a higher permeability than air. The higher the permeability the higher the inductance.

To get the actual Inductance of an inductor we combine the four factors in the formula, inductance is equal to number of turns multiplied by cross sectional area and absolute permeability (UoUr or U) all over length.

formular for inductance