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An electric current can be created in a coil by flux disturbance initiated by another coil in its immediacy or flux change made by the same coil. The flux passing in the coil corresponds to the current in both cases.

Whereby, the current is directly proportional to magnetic flux, or I ∝ ØB.

The common magnetic flux is connected with all the turns for a closely twisted coil of N turns. When the flux through the coil changes, each turn has a part in the generated electromotive force, this is defined using flux linkage, equal to N∅B for a closely twisted coil. In such a case- 

NØB ∝ I

The factor of proportionality here refers to inductance. It is a scalar quantity. The SI unit of inductance is Henry, which is denoted by H and is named after Joseph Henry, an eminent physicist. Joseph Henry was the one to discover electromagnetic induction in the USA, independently of his counterpart Faraday in England. It is influenced by the geometry of the coil and core material properties.

Types of Inductance

There are two types of inductance-

  1. Mutual inductance
  2. Self-inductance

Mutual Inductance 

When an electric current is initiated in a coil by flux disturbances in its immediacy, or when a voltage disturbance in one coil creates a voltage in another coil near it, it is called mutual inductance. The formula to calculate mutual inductance is as follows: 

M=(μo.μr.N1.N2.A)L

Here,

N1 = Turns of coil 1

N2 = Turns of coil 2

A = Cross-sectional area in m2

L= Length of the coil in meters

μ0 = Permeability of free space= 4𝜋10-2

μr = permeability of the soft iron core

The area between the coils and the shape of the coils influences the mutual inductance of two coils, solenoids, etc.

Self-inductance 

The second type of induction is self-induction that requires only one device. When the flow of current fluctuates in a device, it also affects that device’s magnetic field, which can create a negative voltage in the same device. It is called self-induction. This negative voltage acts as a second battery to the primary one, opposing the main voltage source and making it work more to do the same task. Henry is the SI unit of self-inductance, denoted by L. 

Self-inductance is affected by the shape of the circuit. Straight wires have a small L, while twisted wires have a large L.

The formula for self-inductance is as follows-

L=NØii

Where, 

N= number of turns

i= current in the circuit

∅(i)= magnetic flux in the circuit due to the current.

Factors affecting inductance

  • Medium of absorbency between the two coils.
  • The amount of distance between the two coils
  • The magnetic quality of the instrument in the coil that has the flux. 
  • The cross-sectional area that is covered by the coil.
  • The number of turns taken by the coil.
  • The angle of turns the coil makes.

Functions of inductance

The functions of inductance are as follows:

  • All the electric equipment that needs a magnetic field requires mutual induction.
  • It is also common in electric motors.
  • Self-inductance is used in tuning circuits, sensors, induction motors, choked metal detectors, and traffic lights. 
  • The mutual inductance of a transformer is known as the coefficient of coupling. It measures the power transmission efficiency from major coils to minor coils. 
  • Mutual inductance is responsible for affecting or modifying the current and voltage in the secondary coil. 
  • One of the functions of mutual induction is the formation of eddy current and generation in the test material. 
  • Self-inductance is used to store energy in a device. 

Distinction Between Self-Inductance and Mutual Inductance

Mutual-Inductance V/s Self-Inductance

  • When voltage disturbances in one coil create a voltage in another coil near it, it is known as mutual inductance. 
  • When an electric current is created in a coil by flux change initiated by the same coil, it is called self-inductance. 
  • When the coil’s main current falls, the induced current of the other coil defies the fall of current in the coil in mutual inductance.
  • When the coil’s main current falls , the secondary current defies the decay of current in the coil in self-inductance.
  • When the major current of the coil rises, the induced current of the other coil opposes the increase of current in the coil.
  • When the major current of the coil rises, the secondary current opposes the increase of current in the coil.
  • Mutual inductance requires two coils.
  • Self-inductance uses one coil.
  • The formula for mutual inductance is M=(μo.μr.N1.N2.A)L.
  • The formula needed to calculate self-inductance is L=NØii.

Conclusion

Inductance is described as the introduction of current in a coil caused by the interference in the flux of the same coil or one near it. It is of two types- mutual inductance and self-inductance. In mutual inductance, the coils become magnetically linked due to changes in magnetic flux. In self-inductance, the magnetic field can be imagined as a concentric circle, in which the circles are connected, opposing the change in current. The SI unit of inductance is Henry, denoted by H. Inductance is a scalar quantity.