Electromagnetic Induction Class 12 Notes Physics Chapter 6 - CBSE

Chapter : 6

What are Electromagnetic Induction ?

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Electromagnetic Induction

The phenomenox of production of emf in a coil, when magnetic flux linked with the coil is changed.

$$\text{Magnetic flux,}\space \phi\space\vec{\text{B}}.\space\vec{\text{A}}=\text{BA}\space \text{cos} \space\theta,$$

where B is the strength of magnetic field, A is the area of surface and θ is the angle which normal to the area makes with the direction of magnetic field.

The SI unit of magnetic flux is weber (Wb).

Faraday’s Laws

First Law : Whenever there is a change in magnetic flux linked with a circuit, an emf is induced in the circuit, till change in flux keeps on changing.
Second Law : The induced emf is directly proportional to the time rate of change of magnetic flux.
Faraday’s laws are the consequence of the conservation of energy.

Induced Emf And Current

Faraday’s second law of electromagnetic induction gives the magnitude of induced emf/current.

Induced emf, ε =(-dΦ/dt),

where negative sign indicates the direction of ε.

Induced current, i =(induced emf/resistance)=|ε|/R=(dΦ/dt/(R))
Induced emf is measured in volt (V).

Lenz’s Law

This law gives the direction of induced emf. According to Lenz’s law, the polarity of the induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produces it.
Lenz’s law is in accordance with the principle of conservation of energy.

Self Induction

When a current in a coil changes, it induces a back emf in the same coil, this phenomenon is known as self inductance. Self induced emf is given by, ε =(-LdI/dt), where L is the coefficient of self inductance of the coil.
SI unit of self inductance is henry (H)

Mutual Induction

When an emf is produced in a coil because of change in current in a coupled coil, this effect is called mutual inductance.
If Φ is the amount of magnetic flux linked with one coil (primary) when a current I flows through the other (secondary) coil, then Φ = MI, where M is coefficient of mutual inductance of the two coils. Emf induced in the secondary coil is, ε = –M(dI/dt)
SI unit of mutual inductance is henry (H)

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