electromagnet (redirected from Electro-magnet)

electromagnet, device in which magnetism is produced by an electric current. Any electric current produces a magnetic field, but the field near an ordinary straight conductor is rarely strong enough to be of practical use. A strong field can be produced if an insulated wire is wrapped around a soft iron core and a current passed through the wire. The strength of the magnetic field produced by such an electromagnet depends on the number of coils of wire, the magnitude of the current, and the magnetic permeability of the core material; a strong field can be produced from a small current if a large number of turns of wire are used. Unlike the materials from which permanent magnets are made, the soft iron in the core of an electromagnet retains little of the magnetism induced in it by the current after the current has been turned off. This property makes it more useful than a permanent magnet in many applications. Electromagnets are used to lift large masses of magnetic materials, such as scrap iron. They are essential to the design of the electric generator and electric motor and are also employed in doorbells, circuit breakers, television receivers, loudspeakers, atomic particle accelerators, and electromagnetic brakes and clutches. Electromagnetic propulsion systems can provide motive power for spacecraft. Electromagnets are also essential to magnetic levitation systems. Such systems often use a special kind of electromagnet whose coil is made of a superconducting metal. Because the coils of a superconducting electromagnet offers no resistance to the flow of electricity, no energy is wasted by the development of heat, and the magnetic field produced by the magnet can be very strong. Superconducting magnets are used in magnetic-resonance imaging, and can also be used for energy storage. The first practical electromagnet was invented early in the 19th cent. by William Sturgeon.

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electromagnet

Device consisting of a core of magnetic material such as iron, surrounded by a coil through which an electric current is passed to magnetize the core. When the current is stopped, the core is no longer magnetized. Electromagnets are particularly useful wherever controllable magnets are required, as in devices in which the magnetic field is to be varied, reversed, or switched on and off. Suitably designed magnets can lift many times their own weight and are used in steelworks and scrap yards to lift loads of metal. Other devices that utilize electromagnets include particle accelerators, telephone receivers, loudspeakers, and televisions.

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electromagnet

A magnet that is energized by electricity. A coil of wire is wrapped around an iron core. When current flows in the wire, the core generates an energy called "magnetic flux."

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electromagnet

a magnet consisting of an iron or steel core wound with a coil of wire, through which a current is passed

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Electromagnet

A soft-iron core that is magnetized by passing a current through a coil of wire wound on the core. Electromagnets are used to lift heavy masses of magnetic material and to attract movable magnetic parts of electric devices, such as solenoids, relays, and clutches.

The difference between cores of an electromagnet and a permanent magnet is in the retentivity of the material used. Permanent magnets, initially magnetized by placing them in a coil through which current is passed, are made of retentive (magnetically “hard”) materials which maintain the magnetic properties for a long period of time after being removed from the coil. Electromagnets are meant to be devices in which the magnetism in the cores can be turned on or off. Therefore, the core material is nonretentive (magnetically “soft”) material which maintains the magnetic properties only while current flows in the coil. All magnetic materials have some retentivity, called residual magnetism; the difference is one of degree.

In an engineering sense the word electromagnet does not refer to the electromagnetic forces incidentally set up in all devices in which an electric current exists, but only to those devices in which the current is primarily designed to produce this force, as in solenoids, relay coils, electromagnetic brakes and clutches, and in tractive and lifting or holding magnets and magnetic chucks.

Electromagnets may be divided into two classes: traction magnets, in which the pull is to be exerted over a distance and work is done by reducing the air gap; and lifting or holding magnets, in which the material is initially placed in contact with the magnet. Examples of the latter type are magnetic chucks and circular lifting magnets. For examples of the first type. See Brake, Clutch, Relay