Faraday's law of induction
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Faraday's law of induction (more generally, the law of electromagnetic induction) states that the induced emf (electromotive force) in a closed loop equals the negative of the time rate of change of magnetic flux through the loop. This simply means that the induced emf is proportional to the rate of change of the magnetic flux through a coil. To restate it means:The Voltage induced across a conductor as it moves at right angles through a magnetic field is proportional to the velocity of that moving conductor.
The relation between the rate of change of the magnetic flux through the surface S enclosed by a contour C and the electric field along the contour:
where E is the electric field, dl is an infinitesimal element of the contour C and B is the magnetic flux density. The directions of the contour C and of 
are assumed to be related by the right-hand rule.
Equivalently, the differential form of Faraday's law is
which is one of the Maxwell equations.
In the case of an inductor coil where the electric wire makes N turns, the formula becomes:
where emf is the induced electromotive force and dΦ/dt is the time-rate of change of magnetic flux Φ. The direction of the electromotive force (the negative sign in the above formula) was first given by Lenz's law.
This principle is used for measuring flow of electrically conductive liquids and slurris and such instruments are called Magnetic Flow Meters. The induced voltage U generated in the magnetic field B due to conductive liquid moving at velocity v is thus given by:
,
where L is the distance between electrodes in the magnetic flow meter.
Faraday's law, along with the other laws of electromagnetism, was later incorporated into Maxwell's equations, unifying all of electromagnetism.
Faraday's law of induction is based on Michael Faraday's experiments in 1831. The effect was also discovered by Joseph Henry at about the same time, but Faraday published first.[1][2]
[edit] Practical Demonstration
Several video practical demonstrations of Faraday's Law can be watched over the internet. A brief but informative video may be watched at EduMation.
[edit] See also
- Magnetic flux density
- Ampère's law
- Stokes' theorem
- Vector calculus
- Moving magnet and conductor problem
[edit] References
- ^ Ulaby, Fawwaz (2001-01-31). Fundamentals of Applied Electromagnetics, 2nd edition, Prentice Hall, p. 232. ISBN 0-13-032931-2.
- ^ Joseph Henry. Distinguished Members Gallery, National Academy of Sciences. Retrieved on November 30, 2006.
