Faraday's law of induction
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For applications and consequences of the law, see Electromagnetic induction.
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current which flows through the
small coil (A), creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out
of the large coil (B), the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer (G).[1]
Faraday's law of induction (briefly, Faraday's law) is a basic law
of electromagnetism predicting how a magnetic field will interact with
an electric circuit to produce an electromotive force (emf)—a phenomenon
known as electromagnetic induction. It is the fundamental operating principle
of transformers, inductors, and many types
of electrical motors, generators and solenoids. [2][3]
The Maxwell–Faraday equation (listed as one of Maxwell's equations)
describes the fact that a spatially varying (and also possibly time-varying,
depending on how a magnetic field varies in time) electric field always
accompanies a time-varying magnetic field, while Faraday's law states that
there is emf (electromotive force, defined as electromagnetic work done on a
unit charge when it has traveled one round of a conductive loop) on the
conductive loop when the magnetic flux through the surface enclosed by the
loop varies in time.
Faraday's law had been discovered and one aspect of it (transformer emf) was
formulated as the Maxwell–Faraday equation later. The equation of Faraday's
law can be derived by the Maxwell–Faraday equation (describing transformer
emf) and the Lorentz force (describing motional emf). The integral form of the
Maxwell–Faraday equation describes only the transformer emf, while the
equation of Faraday's law describes both the transformer emf and the motional
emf.
History[edit]
, A diagram of Faraday's iron ring apparatus. The changing magnetic flux of the left coil induces a current in the right coil. [4]
Electromagnetic induction was discovered independently by Michael
Faraday in 1831 and Joseph Henry in 1832. Faraday was the first to publish [5]
the results of his experiments. In Faraday's first experimental demonstration
[6][7]
of electromagnetic induction (August 29, 1831), he wrapped two wires around [8]
opposite sides of an iron ring (torus) (an arrangement similar to a
modern toroidal transformer). Based on his assessment of recently discovered
properties of electromagnets, he expected that when current started to flow in
one wire, a sort of wave would travel through the ring and cause some
electrical effect on the opposite side. He plugged one wire into
a galvanometer, and watched it as he connected the other wire to a battery.
Indeed, he saw a transient current (which he called a "wave of electricity")
when he connected the wire to the battery, and another when he disconnected
it. This induction was due to the change in magnetic flux that occurred
[9]: 182–183
when the battery was connected and disconnected. Within two months, [4]
Faraday had found several other manifestations of electromagnetic induction.
For example, he saw transient currents when he quickly slid a bar magnet in
and out of a coil of wires, and he generated a steady (DC) current by rotating a
copper disk near the bar magnet with a sliding electrical lead ("Faraday's
disk"). [9]: 191–195
Faraday's disk, the first electric generator, a type of homopolar generator.
Michael Faraday explained electromagnetic induction using a concept he
called lines of force. However, scientists at the time widely rejected his
theoretical ideas, mainly because they were not formulated mathematically. [9]:
An exception was James Clerk Maxwell, who in 1861–62 used Faraday's
510
ideas as the basis of his quantitative electromagnetic theory. In Maxwell's [9]: 510 [10][11]
papers, the time-varying aspect of electromagnetic induction is expressed as a
differential equation which Oliver Heaviside referred to as Faraday's law even
though it is different from the original version of Faraday's law, and does not
describe motional emf. Heaviside's version (see Maxwell–Faraday equation
Jump to navigationJump to search
For applications and consequences of the law, see Electromagnetic induction.
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current which flows through the
small coil (A), creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out
of the large coil (B), the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer (G).[1]
Faraday's law of induction (briefly, Faraday's law) is a basic law
of electromagnetism predicting how a magnetic field will interact with
an electric circuit to produce an electromotive force (emf)—a phenomenon
known as electromagnetic induction. It is the fundamental operating principle
of transformers, inductors, and many types
of electrical motors, generators and solenoids. [2][3]
The Maxwell–Faraday equation (listed as one of Maxwell's equations)
describes the fact that a spatially varying (and also possibly time-varying,
depending on how a magnetic field varies in time) electric field always
accompanies a time-varying magnetic field, while Faraday's law states that
there is emf (electromotive force, defined as electromagnetic work done on a
unit charge when it has traveled one round of a conductive loop) on the
conductive loop when the magnetic flux through the surface enclosed by the
loop varies in time.
Faraday's law had been discovered and one aspect of it (transformer emf) was
formulated as the Maxwell–Faraday equation later. The equation of Faraday's
law can be derived by the Maxwell–Faraday equation (describing transformer
emf) and the Lorentz force (describing motional emf). The integral form of the
Maxwell–Faraday equation describes only the transformer emf, while the
equation of Faraday's law describes both the transformer emf and the motional
emf.
History[edit]
, A diagram of Faraday's iron ring apparatus. The changing magnetic flux of the left coil induces a current in the right coil. [4]
Electromagnetic induction was discovered independently by Michael
Faraday in 1831 and Joseph Henry in 1832. Faraday was the first to publish [5]
the results of his experiments. In Faraday's first experimental demonstration
[6][7]
of electromagnetic induction (August 29, 1831), he wrapped two wires around [8]
opposite sides of an iron ring (torus) (an arrangement similar to a
modern toroidal transformer). Based on his assessment of recently discovered
properties of electromagnets, he expected that when current started to flow in
one wire, a sort of wave would travel through the ring and cause some
electrical effect on the opposite side. He plugged one wire into
a galvanometer, and watched it as he connected the other wire to a battery.
Indeed, he saw a transient current (which he called a "wave of electricity")
when he connected the wire to the battery, and another when he disconnected
it. This induction was due to the change in magnetic flux that occurred
[9]: 182–183
when the battery was connected and disconnected. Within two months, [4]
Faraday had found several other manifestations of electromagnetic induction.
For example, he saw transient currents when he quickly slid a bar magnet in
and out of a coil of wires, and he generated a steady (DC) current by rotating a
copper disk near the bar magnet with a sliding electrical lead ("Faraday's
disk"). [9]: 191–195
Faraday's disk, the first electric generator, a type of homopolar generator.
Michael Faraday explained electromagnetic induction using a concept he
called lines of force. However, scientists at the time widely rejected his
theoretical ideas, mainly because they were not formulated mathematically. [9]:
An exception was James Clerk Maxwell, who in 1861–62 used Faraday's
510
ideas as the basis of his quantitative electromagnetic theory. In Maxwell's [9]: 510 [10][11]
papers, the time-varying aspect of electromagnetic induction is expressed as a
differential equation which Oliver Heaviside referred to as Faraday's law even
though it is different from the original version of Faraday's law, and does not
describe motional emf. Heaviside's version (see Maxwell–Faraday equation
