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Lenz's law states that the direction of the electric current induced in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in the initial magnetic field. It is named after physicist Heinrich Lenz, who formulated it in 1834. [1]
[22] [23] This is believed to be a unique example in physics of where such a fundamental law is invoked to explain two such different phenomena. [ 24 ] Albert Einstein noticed that the two situations both corresponded to a relative movement between a conductor and a magnet, and the outcome was unaffected by which one was moving.
By Lenz's law, an eddy current creates a magnetic field that opposes the change in the magnetic field that created it, and thus eddy currents react back on the source of the magnetic field. For example, a nearby conductive surface will exert a drag force on a moving magnet that opposes its motion, due to eddy currents induced in the surface by ...
the constant is the permeability of free space, commonly called , divided by ; in the absence of magnetically reactive insulation the value 200 is exact when using the classical definition of μ 0 = 4π × 10 −7 H/m, and correct to 7 decimal places when using the 2019-redefined SI value of μ 0 = 1.256 637 062 12 (19) × 10 −6 H/m.
A separate CDR is generated for each party to be charged. Entries on CDRs use a {category, usage} syntax. Usage units can be bits (e.g. user downloaded a 1MB movie), seconds (e.g. user downloaded 1 minute of a movie), or other units (e.g. user downloaded 1 movie).
That is, the back-EMF is also due to inductance and Faraday's law, but occurs even when the motor current is not changing, and arises from the geometric considerations of an armature spinning in a magnetic field. This voltage is in series with and opposes the original applied voltage and is called "back-electromotive force" (by Lenz's law).
According to Lenz's law, this opposes the external field. Diamagnets are materials with a magnetic permeability less than μ 0 (a relative permeability less than 1). Consequently, diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field.
The theory of special relativity plays an important role in the modern theory of classical electromagnetism.It gives formulas for how electromagnetic objects, in particular the electric and magnetic fields, are altered under a Lorentz transformation from one inertial frame of reference to another.