Electromagnetic induction

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Electromagnetic induction is not to be confused with "Magnetic induction", which usually refers to Magnetic field.

Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux.

Discovery

Michael Faraday is generally credited with having discovered the induction phenomenon in [1831 though it may have been anticipated by the work of Francesco Zantedeschi in 1829.

Findings

Faraday found that the electromotive force (EMF) produced around a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path.

In practice, this means that an electrical current will be induced in any closed circuit when the magnetic flux through a surface bounded by the conductor changes. This applies whether the field itself changes in strength or the conductor is moved through it.

Electromagnetic induction underlies the operation of generators, induction motors, transformers, and most other electrical machines.

Faraday's law of electromagnetic induction states that:

$\mathcal{E} = {-{d\Phi_B} \over dt}$ ,

where

$\mathcal{E}$ is the electromotive force (emf) in volts

Φ_B is the magnetic flux in webers

For the common, but special case, of a coil of wire, comprised of N loops with the same area, Faraday's law of electromagnetic induction states that

$\mathcal{E} = - N{{d\Phi_B} \over dt}$

where

$\mathcal{E}$ is the electromotive force (emf) in volts

N is the number of turns of wire

Φ_B is the magnetic flux in webers through a single loop.

Further, Lenz's law gives the direction of the induced emf, thus:

The emf induced in an electric circuit always acts in such a direction that the current it drives around the circuit opposes the change in magnetic flux which produces the emf.

Lenz's law is therefore responsible for the minus sign in the above equation.

Applications

The principles of electromagnetic induction are applied in many devices and systems, including:

• Induction motors
• Electrical generators
• Transformers
• Electromagnetic forming
• Magnetic flow meters
• Transcranial magnetic stimulation