The ampere-turn (symbol A⋅t) is the
MKS (metre–kilogram–second) unit of
magnetomotive force
In physics, the magnetomotive force (abbreviated mmf or MMF, symbol \mathcal F) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, Hopkinson's law. It is the property of certain substances or phenomena that give ...
(MMF), represented by a
direct current
Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...
of one
ampere
The ampere ( , ; symbol: A), often shortened to amp,SI supports only the use of symbols and deprecates the use of abbreviations for units. is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 c ...
flowing in a single-turn loop. ''Turns'' refers to the
winding number
In mathematics, the winding number or winding index of a closed curve in the plane (mathematics), plane around a given point (mathematics), point is an integer representing the total number of times that the curve travels counterclockwise aroun ...
of an electrical conductor composing an
electromagnetic coil
An electromagnetic coil is an electrical Electrical conductivity, conductor such as a wire in the shape of a wiktionary:coil, coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric curre ...
.
For example, a current of flowing through a coil of 10 turns produces an MMF of .
The corresponding physical quantity is ''NI'', the product of the
number of turns
A number is a mathematical object used to count, measure, and label. The most basic examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can ...
, ''N'', and the current, ''I''; it has been used in industry, specifically, US-based
coil-making industries.
By maintaining the same current and increasing the number of loops or turns of the coil, the strength of the magnetic field increases because each loop or turn of the coil sets up its own magnetic field. The magnetic field unites with the fields of the other loops to produce the field around the entire coil, making the total magnetic field stronger.
The strength of the magnetic field is not linearly related to the ampere-turns when a magnetic material is used as a part of the system. Also, the material within the magnet carrying the magnetic flux "saturates" at some point, after which adding more ampere-turns has little effect.
The ampere-turn corresponds to
gilberts, the corresponding
CGS unit.
In
Thomas Edison
Thomas Alva Edison (February11, 1847October18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventions, ...
's laboratory
Francis Upton
Francis Robbins Upton (1852 in Peabody, Massachusetts – March 10, 1921, in Orange, New Jersey) was an American physicist and mathematician. Upton worked alongside Thomas Edison in the development of incandescent light bulbs, electric generators ...
was the lead mathematician. Trained with
Helmholtz
Hermann Ludwig Ferdinand von Helmholtz (; ; 31 August 1821 – 8 September 1894; "von" since 1883) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The ...
in Germany, he used ''weber'' as the name of the unit of current, modified to ''ampere'' later:
:When conducting his investigations, Upton always noted the Weber turns and with his other data had all that was necessary to put the results of his work in proper form.
:He discovered that a Weber turn (that is, an ampere turn) was a constant factor, a given number of which always produced the same effect magnetically.
See also
*
Inductance
Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The electric current produces a magnetic field around the conductor. The magnetic field strength depends on the magnitude of the ...
*
Solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whos ...
References
{{DEFAULTSORT:Ampere-Turn
Units of measurement
Magnetism