Chapter : 6

What are Electromagnetic Induction ?

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)