Electromagnet

Electromagnet is a device that has magnetic properties only when an electric current is

applied to it, the electromagnet is an essential part of electric generators and motors it is also

used in many other devices, including electric bells, tape recorders, circuit breakers, and

scientific instruments called particle accelerators. Large electromagnets, attached to cranes, are

used to lift huge loads of metal.

The simplest electromagnet is a coil of insulated wire the magnetism it produces is

weak. However, for practical purposes, the wire is wound around an iron core, greatly

increasing the magnetic strength.

In 1820, Hans Christian Oersted, a Danish physicist, discovered that an electric current

has magnetic properties William Sturgeon, an English physicist who used the principle of

Oersted, made the first electromagnet in 1823, Joseph Henry, a United States physicist, greatly

improved Sturgeon's design in the late 1820's.

Special Types of Electromagnets

A Relay is an electromagnet used as a switch to permit one electric circuit to control the

operation of one or more additional circuits, the switch contacts are moved by the

electromagnet rather than by hand. Relays are used in many control devices, including furnace

controls and automobile electrical circuits.

A Solenoid can be used as a relay or to control mechanical equipment it consists of a coil

wound on a nonmagnetic cylinder, inside of which is an iron plunger free to move. When

current is applied, the plunger is attracted into the coil. With this action, the plunger either

closes an electric switch or pushes against a lever.

Source: http://science.howstuffworks.com/electromagnet-info.htm accessed 02 December 2012.