1. 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.