Solenoid

Magnetic field demonstration with solenoid-shaped insulated wire and iron filings

A solenoid (/ˈsoʊlənɔɪd/^[1]) is a type of electromagnet formed by a helical coil of wire whose length is substantially greater than its diameter,^[2] which generates a controlled magnetic field. The coil can produce a uniform magnetic field in a volume of space when an electric current is passed through it.

André-Marie Ampère coined the term solenoid in 1823, having conceived of the device in 1820.^[3] The French term originally created by Ampère is solénoïde, which is a French transliteration of the Greek word σωληνοειδὴς which means tubular.

The helical coil of a solenoid does not necessarily need to revolve around a straight-line axis; for example, William Sturgeon's electromagnet of 1824 consisted of a solenoid bent into a horseshoe shape (similarly to an arc spring).

Solenoids provide magnetic focusing of electrons in vacuums, notably in television camera tubes such as vidicons and image orthicons. Electrons take helical paths within the magnetic field. These solenoids, focus coils, surround nearly the whole length of the tube.

^ "solenoid: Meaning in the Cambridge English Dictionary". dictionary.cambridge.org. Archived from the original on 16 January 2017. Retrieved 16 January 2017.
^ or equivalently, the diameter of the coil is assumed to be infinitesimally small (Ampère 1823, p. 267: "des courants électriques formants de très-petits circuits autour de cette ligne, dans des plans infiniment rapprochés qui lui soient perpendiculaires").
^ Session of the Académie des sciences of 22 December 1823, published in print in: Ampère, "Mémoire sur la théorie mathématique des phénomènes électro-dynamiques", Mémoires de l'Académie royale des sciences de l'Institut de France 6 (1827), Paris, F. Didot, pp. 267ff. (and figs. 29–33). "l'assemblage de tous les circuits qui l'entourent [viz. l'arc], assemblage auquel j'ai donné le nom de solénoïde électro-dynamique, du mot grec σωληνοειδὴς, dont la signification exprime précisement ce qui a la forme d'un canal, c'est-à-dire la surface de cette forme sur laquelle se trouvent tous les circuits." (p. 267). English translation: "the assembly of all the circuits that surround it [viz. the arc], assembly to which I gave the name electro-dynamic solenoid, from the Greek word σωληνοειδὴς, whose meaning precisely expresses what has the shape of a channel, that is to say the surface of this shape on which all the circuits are located".

[1] "solenoid: Meaning in the Cambridge English Dictionary". dictionary.cambridge.org. Archived from the original on 16 January 2017. Retrieved 16 January 2017.

[2] r equivalently, the diameter of the coil is assumed to be infinitesimally small (Ampère 1823, p. 267: "des courants électriques formants de très-petits circuits autour de cette ligne, dans des plans infiniment rapprochés qui lui soient perpendiculaires").

[3] Session of the Académie des sciences of 22 December 1823, published in print in: Ampère, "Mémoire sur la théorie mathématique des phénomènes électro-dynamiques", Mémoires de l'Académie royale des sciences de l'Institut de France 6 (1827), Paris, F. Didot, pp. 267ff. (and figs. 29–33). "l'assemblage de tous les circuits qui l'entourent [viz. l'arc], assemblage auquel j'ai donné le nom de solénoïde électro-dynamique, du mot grec σωληνοειδὴς, dont la signification exprime précisement ce qui a la forme d'un canal, c'est-à-dire la surface de cette forme sur laquelle se trouvent tous les circuits." (p. 267). English translation: "the assembly of all the circuits that surround it [viz. the arc], assembly to which I gave the name electro-dynamic solenoid, from the Greek word σωληνοειδὴς, whose meaning precisely expresses what has the shape of a channel, that is to say the surface of this shape on which all the circuits are located".

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