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solenoid

A solenoid (,) is a type of electromagnet.
In electromagnetic technology, a solenoid is an actuator assembly with a sliding ferromagnetic plunger inside the coil. Without power, the plunger extends for part of its length outside the coil; applying power pulls the plunger into the coil. Electromagnets with fixed cores are not considered solenoids.
Typically, it has a multiturn coil of magnet wire surrounded by a frame, which is also a magnetic flux carrier to enhance its efficiency.
In simple terms, a solenoid converts electrical energy into mechanical work.
Academic analysis focuses on a helix, such as shown above. The helix 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. Such 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.
The term solenoid was coined in 1823 by André-Marie Ampère to designate a helical coil.In the study of electromagnetism, a solenoid is a coil whose length is substantially greater than its diameter.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.
In engineering, the term may also refer to a variety of transducer devices that convert energy into linear motion, more sophisticated than simple two–position actuators.The term "solenoid" also often refers to a solenoid valve, an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve, or a solenoid switch, which is a specific type of relay that internally uses an electromechanical solenoid to operate an electrical switch; for example, an automobile starter solenoid or linear solenoid. Solenoid bolts, a type of electromechanical locking mechanism, also exist.
The term solenoid also can refer to any device that converts electrical energy to mechanical energy using a solenoid. The device creates a magnetic field from electric current, and uses the magnetic field to create linear motion.

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