Electromagnet

A simple electromagnet consisting of a coil of wire wrapped around an iron core. A core of ferromagnetic material like iron serves to increase the magnetic field created.  The strength of magnetic field generated is proportional to the amount of current through the winding.
Magnetic field produced by a solenoid (coil of wire). This drawing shows a cross section through the center of the coil. The crosses are wires in which current is moving into the page; the dots are wires in which current is moving up out of the page.
Industrial electromagnet lifting scrap iron, 1914
Current (I) through a wire produces a magnetic field (B). The field is oriented according to the right-hand rule.
The magnetic field lines of a current-carrying loop of wire pass through the center of the loop, concentrating the field there
The magnetic field generated by passing a current through a coil
Cross section of lifting electromagnet like that in above photo, showing cylindrical construction. The windings (C) are flat copper strips to withstand the Lorentz force of the magnetic field. The core is formed by the thick iron housing (D) that wraps around the windings.
Large aluminum busbars carrying current into the electromagnets at the LNCMI (Laboratoire National des Champs Magnétiques Intenses) high field laboratory.
The most powerful electromagnet in the world, the 45 T hybrid Bitter-superconducting magnet at the US National High Magnetic Field Laboratory, Tallahassee, Florida, USA
A hollow tube type of explosively pumped flux compression generator. The hollow copper tube acts like a single turn secondary winding of a transformer; when the pulse of current from the capacitor in the windings creates a pulse of magnetic field, this creates a strong circumferential current in the tube, trapping the magnetic field lines within. The explosives then collapse the tube, reducing its diameter, and the field lines are forced closer together increasing the field.

Type of magnet in which the magnetic field is produced by an electric current.

- Electromagnet
A simple electromagnet consisting of a coil of wire wrapped around an iron core. A core of ferromagnetic material like iron serves to increase the magnetic field created.  The strength of magnetic field generated is proportional to the amount of current through the winding.

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A magnet made of alnico, a ferromagnetic iron alloy, with its keeper

Ferromagnetism

Basic mechanism by which certain materials form permanent magnets, or are attracted to magnets.

Basic mechanism by which certain materials form permanent magnets, or are attracted to magnets.

A magnet made of alnico, a ferromagnetic iron alloy, with its keeper
Electromagnetic dynamic magnetic domain motion of grain-oriented electrical silicon steel
Kerr micrograph of metal surface showing magnetic domains, with red and green stripes denoting opposite magnetization directions
Moving domain walls in a grain of silicon steel caused by an increasing external magnetic field in the "downward" direction, observed in a Kerr microscope. White areas are domains with magnetization directed up, dark areas are domains with magnetization directed down.

Ferromagnetism is very important in industry and modern technology and is the basis for many electrical and electromechanical devices such as electromagnets, electric motors, generators, transformers, and magnetic storage such as tape recorders, and hard disks, and nondestructive testing of ferrous materials.

A "horseshoe magnet" made of alnico, an iron alloy. The magnet, made in the shape of a horseshoe, has the two magnetic poles close together. This shape creates a strong magnetic field between the poles, allowing the magnet to pick up a heavy piece of iron.

Magnet

Material or object that produces a magnetic field.

Material or object that produces a magnetic field.

A "horseshoe magnet" made of alnico, an iron alloy. The magnet, made in the shape of a horseshoe, has the two magnetic poles close together. This shape creates a strong magnetic field between the poles, allowing the magnet to pick up a heavy piece of iron.
Magnetic field lines of a solenoid electromagnet, which are similar to a bar magnet as illustrated below with the iron filings
Iron filings that have oriented in the magnetic field produced by a bar magnet
Field of a cylindrical bar magnet computed accurately
Hard disk drives record data on a thin magnetic coating
Magnetic hand separator for heavy minerals
Magnets have many uses in toys. M-tic uses magnetic rods connected to metal spheres for construction.
A stack of ferrite magnets
Ovoid-shaped magnets (possibly Hematine), one hanging from another
Field lines of cylindrical magnets with various aspect ratios

An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops.

Joseph Henry

American scientist who served as the first Secretary of the Smithsonian Institution.

American scientist who served as the first Secretary of the Smithsonian Institution.

Signature
Historical marker in Academy Park (Albany) commemorating Henry's work with electricity.
Henry, taken between 1865 and 1878, possibly by Mathew Brady.
Henry's grave, Oak Hill Cemetery, Washington, D.C.
Statue of Henry in front of the Smithsonian Institution
A bronze statue of Henry stands on the rotunda of the U.S. Library of Congress.

Henry developed the electromagnet into a practical device.

The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.

Magnetic field

Vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

Vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.
Right hand grip rule: a current flowing in the direction of the white arrow produces a magnetic field shown by the red arrows.
A Solenoid with electric current running through it behaves like a magnet.
A sketch of Earth's magnetic field representing the source of the field as a magnet. The south pole of the magnetic field is near the geographic north pole of the Earth.
One of the first drawings of a magnetic field, by René Descartes, 1644, showing the Earth attracting lodestones. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
Hans Christian Ørsted, Der Geist in der Natur, 1854

Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time.

Kellogg and Rice in 1925 holding the large driver of the first moving-coil cone loudspeaker

Loudspeaker

[[File:Electrodynamic-loudspeaker.png|thumb|Hi-fi speaker system for home use with three types of dynamic drivers 1. Mid-range driver

[[File:Electrodynamic-loudspeaker.png|thumb|Hi-fi speaker system for home use with three types of dynamic drivers 1. Mid-range driver

Kellogg and Rice in 1925 holding the large driver of the first moving-coil cone loudspeaker
A four-way, high fidelity loudspeaker system. Each of the four drivers outputs a different frequency range; the fifth aperture at the bottom is a bass reflex port.
Exploded view of a dome tweeter
Electronic symbol for a speaker
A passive crossover
A bi-amplified system with an active crossover
An unusual three-way speaker system. The cabinet is narrow to raise the frequency where a diffraction effect called the "baffle step" occurs.
A three-way loudspeaker that uses horns in front of each of the three drivers: a shallow horn for the tweeter, a long, straight horn for mid frequencies and a folded horn for the woofer
Two-way binding posts on a loudspeaker, connected using banana plugs.
A 4-ohm loudspeaker with two pairs of binding posts capable of accepting bi-wiring after the removal of two metal straps.
HP Roar Wireless Speaker
Specifications label on a loudspeaker
Polar plots of a four-driver industrial columnar public address loudspeaker taken at six frequencies. Note how the pattern is nearly omnidirectional at low frequencies, converging to a wide fan-shaped pattern at 1 kHz, then separating into lobes and getting weaker at higher frequencies
Moving iron speaker
A piezoelectric buzzer. The white ceramic piezoelectric material can be seen fixed to a metal diaphragm.
Magnetostatic loudspeaker
Schematic showing an electrostatic speaker's construction and its connections. The thickness of the diaphragm and grids has been exaggerated for the purpose of illustration.
In Heil's air motion transducer, current through the membrane 2 causes it to move left and right in magnetic field 6, moving air in and out along directions 8; barriers 4 prevent air from moving in unintended directions.
Plasma speaker

These first loudspeakers used electromagnets, because large, powerful permanent magnets were generally not available at a reasonable price.

William Sturgeon

William Sturgeon

William Sturgeon
The first artificial electromagnet, invented by Sturgeon in 1824. Sturgeon's original drawing from his 1824 paper to the British Royal Society of Arts, Manufactures, and Commerce. The magnet was made of 18 turns of bare copper wire (insulated wire had not yet been invented).

William Sturgeon (22 May 1783 – 4 December 1850) was an English physicist and inventor who made the first electromagnets, and invented the first practical British electric motor.

Longitudinal recording and perpendicular recording, two types of writing heads on a hard disk.

Magnetic storage

Storage of data on a magnetized medium.

Storage of data on a magnetized medium.

Longitudinal recording and perpendicular recording, two types of writing heads on a hard disk.
The programmable calculators of the HP-41-series (from 1979) could store data via an external magnetic tape storage device on microcassettes
Hard drives use magnetic memory to store giga- and terabytes of data in computers.

Early HDDs used an electromagnet both to magnetise the region and to then read its magnetic field by using electromagnetic induction.

An illustration of a solenoid

Solenoid

An illustration of a solenoid
Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
Figure 1: An infinite solenoid with three arbitrary Ampèrian loops labelled a, b, and c. Integrating over path c demonstrates that the magnetic field inside the solenoid must be radially uniform.
The picture shows how Ampère's law can be applied to the solenoid
Magnetic field line and density created by a solenoid with surface current density
Examples of irregular solenoids (a) sparse solenoid, (b) varied pitch solenoid, (c) non-cylindrical solenoid

A solenoid is a type of electromagnet formed by a helical coil of wire whose length is substantially greater than its diameter, which generates a controlled magnetic field.

(left) Eddy currents ( I, red ) within a solid iron transformer core. (right) Making the core out of thin laminations parallel to the field ( B, green ) with insulation between them reduces the eddy currents. In this diagram the field and currents are shown in one direction, but they actually reverse direction with the alternating current in the transformer winding.

Magnetic core

(left) Eddy currents ( I, red ) within a solid iron transformer core. (right) Making the core out of thin laminations parallel to the field ( B, green ) with insulation between them reduces the eddy currents. In this diagram the field and currents are shown in one direction, but they actually reverse direction with the alternating current in the transformer winding.
Typical EI Lamination.
Ferrite rods are simple cylinders of ferrite that can be wound around.
A toroidal core
On the left, a non-adjustable ferrite rod with connection wires glued to the ends. On the right, a molded ferrite rod with holes, with a single wire threaded through the holes.
A ferrite ring on a computer data cable.

A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies.

A relay

Relay

Electrically operated switch.

Electrically operated switch.

A relay
Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts
An automotive-style miniature relay with the dust cover taken off
Telegraph relay contacts and spring
Simple electromechanical relay
Operation without flyback diode, arcing causes degradation of the switch contacts
Operation with flyback diode, arcing in the control circuit is avoided
A small cradle relay often used in electronics. The "cradle" term refers to the shape of the relay's armature
Circuit symbols of relays (C denotes the common terminal in SPDT and DPDT types.)
Latching relay with permanent magnet
A mercury-wetted reed relay
(from top) Single-pole reed switch, four-pole reed switch and single-pole reed relay. Scale in centimeters
Solid-state relays have no moving parts.
25 A and 40 A solid state contactors
A DPDT AC coil relay with "ice cube" packaging
Part of a relay interlocking using UK Q-style miniature plug-in relays
Several 30-contact relays in "Connector" circuits in mid-20th century 1XB switch and 5XB switch telephone exchanges; cover removed on one.

The traditional form of a relay uses an electromagnet to close or open the contacts, but other operating principles have been invented, such as in solid-state relays which use semiconductor properties for control without relying on moving parts.