British electrician, William Sturgeon invented the electromagnet in 1825. The first electromagnet was a horseshoe-shaped piece of iron that was wrapped with a loosely wound coil of several turns. When a current was passed through the coil; the electromagnet became magnetized and when the current was stopped the coil was de-magnetized. Sturgeon displayed its power by lifting nine pounds with a seven-ounce piece of iron wrapped with wires through which the current of a single cell battery was sent. Sturgeon could regulate his electromagnet; this was the beginning of using electrical energy for making useful and controllable machines and laid the foundations for large-scale electronic communications.

Five year later an inventor called Joseph Henry made a far more powerful version of the electromagnet. American, Joseph Henry (1797-1878), demonstrated the potential of Sturgeon's device for long distance communication by sending an electronic current over one mile of wire to activate an electromagnet which caused a bell to strike. Thus the electric telegraph was born.

Iron or steel can be considered as consisting of numerous randomly disposed magnetic units, or domains, which cancel one another so that the piece of metal as a whole exhibits no magnetic polarity (Fig.1). When the iron is magnetized, these domains become aligned in the same direction and thus act in combination to produce overall magnetic properties: the iron has thus become a magnet (Fig.2). This can be done by placing the iron in the field of force of an existing magnet or by placing it within a coil of insulated wire (Fig.3) through which an electric current is passed; in the latter case the coil with its iron core forms an electromagnet. If the core is of soft iron, it loses its magnetism almost immediately after the current in the coil is switched off i.e., when the electromagnet is de-energized.

On the other hand, steel will retain a substantial proportion of the magnetism it acquires and thus form a permanent magnet, in which the magnetic domains persist in retaining their aligned orientation after the external magnetic field which produced this orientation has been removed. The orientation can be disrupted by heating the steel, whereby the magnetic domains revert to their random condition and the steel becomes partly or wholly demagnetized. The electromagnet is based on the fact that an electric current passing through a circular conductor (Fig.4) produces a magnetic field i.e., is surrounded by magnetic lines of force which together from the so-called magnetic flux.

A coil contains of many turns of wire (Fig.5) can be conceived as the superposition of a corresponding number of circular conductors. If the coil is provided with an iron core (Fig.6), the flux density (or magnetic induction) is greatly increased. This is due to the property of ferromagnetism possessed by iron and certain other metals. A ferromagnetic material has a high magnetic permeability (µ), this being the ratio of the magnetic induction (B) in a piece of magnetic material to the external magnetic field strength (H) producing the induction. The permeability of air and nonmagnetic materials is unity.

Fig.5 shows the magnetic field set up by a coil in which a current is flowing. Externally its properties are generally similar to those of a bar magnet, with south and north pole respectively. The highest field strength occurs at the center (Fig.7). As already stated, the presence of a ferromagnetic material in the magnetic field strength of the coil itself by the relation B= µH, where µ denotes the permeability. The permeability may be conceived as the criterion for the increase in the number of magnetic lines of force brought about by the orientation of the magnetic domains in the iron.

In practical terms, the presence of an iron core within the coil makes the magnetic field very much stronger. The permeability varies for different values of the magnetic induction, even for the same material (Fig.8). The magnetic-field strength of the coil increases in proportion to the strength of the current flowing through it; as a result, more and more of the domains in the iron core become aligned until finally they are all oriented in the same direction (Fig.2). The iron is then said to have become magnetically saturated. Any further increase in the magnetic-field strength (H) will produce little or no change in the magnetic induction (B).

Small electromagnets are used in a large variety of electrical equipment. For E.g.: electric bell, the relay, loudspeaker, the telephone etc. There are innumerable other types of apparatus and electrical machinery in which electromagnets play an important role: measuring equipment, television tubes, switch gear, remote-control equipment, tape recorders, signaling devices, telecommunication equipment etc. The magnetic lenses in electron micro scopes are basically electromagnets. Electric motors and generators are of course, very important application of electromagnets. Lifting magnets are used for handling scrap iron, steel plates, etc.; such magnets may have lifting capacities of several tons. Powerful electromagnets play an important part in various branches of research e.g in cyclotrons and similar equipment.

To produce a powerful magnetic field, the electromagnet should have a core which resembles as closely as possible a ring interrupted only by a narrow gap (Fig.10); it is within this gap that the powerful field is developed, especially if the two poles are so shaped as to produce a concentration of the lines of force (Fig.11). Examples of electromagnets embodying this principle and designed to produce high field strengths are illustrated in Figs 12 and Fig. 13. The unit of magnetic-field strength is the oersted, this being the force in dynes which acts on a unit magnetic pole at any point in a magnetic field; the unit of magnetic flux is the weber; the gauss is the unit of magnetic induction.

To achieve high field strengths in large volumes of space, it is necessary to dispense with the iron core: a large and long coil with a large number of windings and a powerful electric current will produce a strong and fairly homogenous magnetic field in its interior. Theoretically it would be possible to increase the field strength to any desired value, but in actual practice the heat evolved in the windings causes major difficulties. Water cooling is usually apply for large magnets: the water circulates through pipes embedded in the windings, or the wires themselves are hollow and conduct both electricity and water.

An interesting application of the electromagnet in research is in the production of extremely low temperatures close to absolute zero (-273 oC) by the adiabatic demagnetization of a paramagnetic salt. The specimen to be cooled is embedded in such a salt, and the latter is cooled in liquid helium (about –269 oC). A strong magnetic field is then applied, which serves to orient all the magnetic dipoles (elementary atomic magnets formed by the orbiting electrons) in the salt, releasing heat from this into the helium, so that the temperature of the salt drops and comes very close to absolute zero.

Electromagnets' main advantage springs from their versatility and flexibility. In an electromagnet, the magnetic field can be turned on and off. This is especially useful for cargo loading applications; cargo can be picked up using an electromagnet, the cargo carried to its ideal location, then easily released by turning off the electricity supply. The magnetic field's strength can also be varied by changing the amount of electric current applied.

The variability of their magnetic field makes electromagnets ideal for applications where magnetic strength requirements frequently change. For instance, electromagnets are used in circuit breakers where an electromagnet 'pulls' open a circuit only if electric current load is approaching dangerous levels.