Mutual Inductance

Chapter-6|Electromagnetic Induction (EMI)| NCERT 12th Physics:

Mutual Inductance:

The phenomenon according to which an opposing EMF is produced in a primary coil as a result of change in current or magnetic flux linked with a neighbouring coil is called mutual induction.


If I₁ is changing, then B in primary coil also changes, B in secondary also changes. Thus magnetic flux in secondary coil changes. So we obtained induced EMF as results induced current is generated in secondary coil.


Let a current I₁ flows in primary coil, due to this current, the magnetic flux linked with each turn of the coil be Φ₂. If N₂ be the number of turns in the secondary coil, then the number of flux linked with the secondary coil will be N₂Φ₂.

This number of flux is proportional to the current I₁, flowing in the primary coil.

Note: M depends upon geometry of two coils,  and their orientation, separation and medium etc.


If on changing the current in primary coil, the EMF induced in the secondary coil is e₂, then according to Faraday’s law

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Mutual Inductance of Two Long Co-axial Solenoid:

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Let current in outer solenoid be i₁, then magnetic field B inside the outer solenoid along the axis

B=  μ₀n₁i₁

Since, these field lines also passes through the inner solenoid, so magnetic flux Φ linked with the each turn of the inner solenoid will be

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