Electromagnetic induction

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Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids.

Michael Faraday is generally credited with the discovery of induction in 1831 though it may have been anticipated by the work of Francesco Zantedeschi in 1829. Around 1830 to 1832 Joseph Henry made a similar discovery, but did not publish his findings until later.

Overview

Main article: Faraday's law of induction

Michael Faraday formulated that 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 electric 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.

In mathematical form, Faraday's law states that:

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

where

$\scriptstyle {\mathcal{E}}$ is the electromotive force

Φ_B is the magnetic flux.

For the special case of a coil of wire, composed of N loops with the same area, the equation becomes

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

A corollary of Faraday's Law, together with Ampère's law and Ohm's law is Lenz's law: 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.

Applications

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

• Current clamp
• Electrical generators
• Electromagnetic forming
• Graphics tablet
• Hall effect meters
• Induction cookers
• Induction motors
• Induction sealing
• Induction welding
• Inductors
• Magnetic flow meters
• Mechanically powered flashlight
• Pickups
• Rowland ring
• Transcranial magnetic stimulation
• Transformers
• Wireless energy transfer

See also

• Eddy current
• Faraday's law of induction
• Gravitational induction
• Inductance
• Maxwell's equations
• Moving magnet and conductor problem

External links

• A free java simulation on motional EMF
• Two videos demonstrating Faraday's and Lenz's laws at EduMation
• Lenz's Law at work.