FACTOID # 21: 15% of Army recruits from South Dakota are Native American, which is roughly the same percentage for female Army recruits in the state.

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Encyclopedia > Magnetic induction

Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic field. Michael Faraday was the first to describe this phenomenon mathematically: he found that the electromotive force (EMF) produced along 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 flow in any closed conductor, 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.

For a coil of wire in a changing magnetic field, Faraday's law of electromagnetic induction states that

where

ε is the electromotive force (emf) in volts

N is the number of turns of wire

Φ is the magnetic flux in webers

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.

• Maxwell's equations for further mathematical treatment.

## Applications

Results from FactBites:

 Electric field/Magnetic induction: Definition (605 words) It is exactly the same for electric field and magnetic induction: the intensity of the field is significant near its source, and decreases rapidly as one moves away from it. However the magnetic induction that we usually measure are in the range of the microtesla (µT), that is to say, one millionth of a tesla. The magnetic permeability of a material is the capability of this material to channel magnetic induction, in other words, to concentrate magnetic flux lines and thus to increase the value of magnetic induction.
 Tengam Engineering, Inc. ::: Magnetic Glossary (1783 words) Magnetic induction is the flux per unit area normal to the direction of the magnetic path. The average value of magnetic induction over the area of the air gap, Ag; or it is the magnetic induction measured at a specific point within the air gap; measured in Gauss. The north pole of a magnet, or compass, is attracted toward the north geographic pole of the earth (which is actually, by definition, a magnetic south pole), and the south pole of a magnet is attracted toward the south geographic pole of the earth.
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