Electromagnetic induction
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Not to be confused with Magnetic inductance.
Alternating electric current flows through the solenoid on the left, producing a changing magnetic field. This field causes, by
electromagnetic induction, an electric current to flow in the wire loop on the right.
Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical
conductor in a changing magnetic field.
Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk
Maxwell mathematically described it as Faraday's law of induction. Lenz's law describes the direction of the induced
field. Faraday's law was later generalized to become the Maxwell–Faraday equation, one of the four Maxwell
equations in his theory of electromagnetism.
Electromagnetic induction has found many applications, including electrical components such
as inductors and transformers, and devices such as electric motors and generators.
History
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current that 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]
, A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil. [2]
Electromagnetic induction was discovered by Michael Faraday, published in 1831.[3][4] It was discovered independently
by Joseph Henry in 1832.[5][6]
In Faraday's first experimental demonstration (August 29, 1831), he wrapped two wires around opposite sides of an
iron ring or "torus" (an arrangement similar to a modern toroidal transformer).[citation needed] Based on his understanding 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. 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.[7] This induction was due to the change
in magnetic flux that occurred when the battery was connected and disconnected.[2] Within two months, Faraday 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").[8]
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 used Faraday's ideas as the basis of his quantitative electromagnetic theory.[9][10][11] In
Maxwell's model, 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 slightly different from Faraday's original
formulation and does not describe motional emf. Heaviside's version (see Maxwell–Faraday equation below) is the
form recognized today in the group of equations known as Maxwell's equations.
In 1834 Heinrich Lenz formulated the law named after him to describe the "flux through the circuit". Lenz's law gives
the direction of the induced emf and current resulting from electromagnetic induction.
Theory
Faraday's law of induction and Lenz's law
Main article: Faraday's law of induction
A solenoid
The longitudinal cross section of a solenoid with a constant electrical current running through it. The magnetic field lines are indicated,
with their direction shown by arrows. The magnetic flux corresponds to the 'density of field lines'. The magnetic flux is thus densest in
the middle of the solenoid, and weakest outside of it.
Jump to navigationJump to search
Not to be confused with Magnetic inductance.
Alternating electric current flows through the solenoid on the left, producing a changing magnetic field. This field causes, by
electromagnetic induction, an electric current to flow in the wire loop on the right.
Electromagnetic or magnetic induction is the production of an electromotive force (emf) across an electrical
conductor in a changing magnetic field.
Michael Faraday is generally credited with the discovery of induction in 1831, and James Clerk
Maxwell mathematically described it as Faraday's law of induction. Lenz's law describes the direction of the induced
field. Faraday's law was later generalized to become the Maxwell–Faraday equation, one of the four Maxwell
equations in his theory of electromagnetism.
Electromagnetic induction has found many applications, including electrical components such
as inductors and transformers, and devices such as electric motors and generators.
History
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current that 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]
, A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil. [2]
Electromagnetic induction was discovered by Michael Faraday, published in 1831.[3][4] It was discovered independently
by Joseph Henry in 1832.[5][6]
In Faraday's first experimental demonstration (August 29, 1831), he wrapped two wires around opposite sides of an
iron ring or "torus" (an arrangement similar to a modern toroidal transformer).[citation needed] Based on his understanding 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. 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.[7] This induction was due to the change
in magnetic flux that occurred when the battery was connected and disconnected.[2] Within two months, Faraday 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").[8]
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 used Faraday's ideas as the basis of his quantitative electromagnetic theory.[9][10][11] In
Maxwell's model, 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 slightly different from Faraday's original
formulation and does not describe motional emf. Heaviside's version (see Maxwell–Faraday equation below) is the
form recognized today in the group of equations known as Maxwell's equations.
In 1834 Heinrich Lenz formulated the law named after him to describe the "flux through the circuit". Lenz's law gives
the direction of the induced emf and current resulting from electromagnetic induction.
Theory
Faraday's law of induction and Lenz's law
Main article: Faraday's law of induction
A solenoid
The longitudinal cross section of a solenoid with a constant electrical current running through it. The magnetic field lines are indicated,
with their direction shown by arrows. The magnetic flux corresponds to the 'density of field lines'. The magnetic flux is thus densest in
the middle of the solenoid, and weakest outside of it.
