This article is about the electromagnet. For the device that converts electricity to mechanical energy, see solenoid (engineering). For other uses, see Solenoid (disambiguation).
An illustration of a solenoidMagnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
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 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).
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