Solenoid

A solenoid (/ˈsoʊlənɔɪd/, from the French solénoïde, a modern coinage based on Greek σωληνοειδής sōlēnoeidḗs 'pipe-shaped') is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. The term was invented in 1823 by André-Marie Ampère to designate a helical coil. A solenoid (/ˈsoʊlənɔɪd/, from the French solénoïde, a modern coinage based on Greek σωληνοειδής sōlēnoeidḗs 'pipe-shaped') is a type of electromagnet, the purpose of which is to generate a controlled magnetic field through a coil wound into a tightly packed helix. The term was invented in 1823 by André-Marie Ampère to designate a helical coil. As a technical term in the study of electromagnetism, a solenoid is a coil that is 'pipe-like' in the sense that its length is substantially greater than its diameter. In practice, the coil is often wrapped around a metallic core, which produces a uniform magnetic field in a volume of space (where some experiment might be carried out) when an electric current is passed through it. A solenoid is a type of electromagnet the purpose of which is to generate a controlled magnetic field. If the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet. The solenoid is not necessarily straight, 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. The term is also often used to refer to a solenoid valve, which is 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 a linear solenoid, which is an electromechanical solenoid. Solenoid bolts, a type of electronic-mechanical locking mechanism, also exist.