The ampere-turn (A⋅t) is the MKS (metre–kilogram–second) unit of

magnetomotive force In physics, the magnetomotive force (mmf) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, often called Ohm's law for magnetic circuits. It is the property of certain substances or phenomena that give rise to ...

(MMF), represented by a

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...

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 elect ...

flowing in a single-turn loop in a vacuum. " Turns" refers to the

winding number In mathematics, the winding number or winding index of a closed curve in the plane around a given point is an integer representing the total number of times that curve travels counterclockwise around the point, i.e., the curve's number of t ...

of an electrical conductor composing an

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...

. For example, a current of flowing through a coil of 10 turns produces an MMF of . 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

gilbert Gilbert may refer to: People and fictional characters * Gilbert (given name), including a list of people and fictional characters *Gilbert (surname), including a list of people Places Australia * Gilbert River (Queensland) * Gilbert River (South ...

s, the corresponding CGS unit. Alternatively, ''NI'' (the product of the number of turns, ''N'', and the current

n amperes N, or n, is the fourteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''en'' (pronounced ), plural ''ens''. History ...

''I'') has been used in industry, specifically, US-based coil-making industries. In

Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 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 inventio ...

'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 generator ...

was the lead mathematician. Trained with Helmholtz 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.

References

{{DEFAULTSORT:Ampere-Turn Units of measurement Magnetism

See also

References