solenoid

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solenoid

(Academy Artworks)

1. A current-carrying coil of wire that acts like a magnet when a current passes through it.
2. An assembly used as a switch, consisting of a coil and a metal core free to slide along the coil axis under the influence of the magnetic field.

[French solénoïde, from Greek sōlēnoeidēs, pipe-shaped : sōlēn, pipe + -oeidēs, -oid.]

An electrically energized coil of insulated wire which produces a magnetic field within the coil. If the magnetic field produced by the coil is used to magnetize and thus attract a plunger or armature to a position within the coil, the device may be considered to be a special form of electromagnet and in this sense the words solenoid and electromagnet are synonymous. In a wider scientific sense the solenoid may be used to produce a uniform magnetic field for various investigations. So long as the length of the coil is much greater than its diameter (20 or more times), the magnetic field at the center of the coil is sensibly uniform, and the field intensity is almost exactly that given by the equation for a solenoid of infinite length.

When used as an electromagnet of the plunger type, the solenoid usually has an iron or steel casing. The casing increases the mechanical force on the plunger and also serves to constrain the magnetic field. The addition of a butt or stop at one end of the solenoid greatly increases the force on the plunger when the distance between the plunger and the stop is small. The illustration shows a steel-clad solenoid with plunger and plunger stop. The relation of force versus distance with and without the stop is also shown. See also Electromagnet.

Steel-clad solenoid. (a) Cross-sectional view. (b) Relation of the force acting on the armature to the displacement of the armature.

An air core coil. Equipped with a movable iron core the solenoid will produce motion. As a result of current through the coil the iron core is pulled into the center of the winding. When the coil is deenergized, a spring pulls the movable core away from the center of the winding. Mechanical devices connected to the movable core are made to move as a result of current through the coil. Example: Electric door locks on some automobiles.

The noun has one meaning:

Meaning #1: a coil of wire around an iron core; becomes a magnet when current passes through the coil