A horseshoe magnet is either a permanent magnet or an

electromagnet An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...

made in the shape of a

horseshoe A horseshoe is a product designed to protect a horse hoof from wear. Shoes are attached on the palmar surface (ground side) of the hooves, usually nailed through the insensitive hoof wall that is anatomically akin to the human toenail, altho ...

(in other words, in a U-shape). The permanent kind has become the most widely recognized symbol for magnets. It is usually depicted as red and marked with 'North' and 'South' poles. Although rendered obsolete in the 1950s by squat, cylindrical magnets made of modern materials, horseshoe magnets are still regularly shown in elementary school textbooks. Historically, they were a solution to the problem of making a compact magnet that does not destroy itself in its own demagnetizing field.

History

In 1819, it was discovered that passing

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

through a piece of

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

deflected a

compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with No ...

needle. Following this discovery, many other experiments surrounding

magnetism Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, ...

were attempted. These experiments culminated in

William Sturgeon William Sturgeon (; 22 May 1783 – 4 December 1850) was an English electrical engineer and inventor who made the first electromagnet and the first practical electric motor. Early life Sturgeon was born on 22 May 1783 in Whittington, near ...

wrapping wire around a horseshoe-shaped piece of iron and running electric current through the wires creating the first horseshoe magnet. This was also the first practical electromagnet and the first magnet that could lift more mass than the magnet itself when the seven-ounce magnet was able to lift nine pounds of

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

. Sturgeon showed that he could regulate the magnetic field of his horseshoe magnet by increasing or decreasing the amount of current being run through the wires. This would lay the groundwork for development of the

electrical telegraph Electrical telegraphy is point-to-point distance communicating via sending electric signals over wire, a system primarily used from the 1840s until the late 20th century. It was the first electrical telecommunications system and the most wid ...

and the future of world-wide

telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

for the next century and more.

Shape

The shape of the magnet was originally created as a replacement for the bar magnet as it makes the magnetic field stronger for a magnet of comparable strength. A horseshoe magnet is stronger because both poles of the magnet are closer to each other and in the same plane which allows the magnetic lines of

flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...

to flow along a more direct path between the poles and concentrates the magnetic field. The shape of the horseshoe magnet also drastically reduces its demagnetization over time. This is due to

coercivity Coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming Magnetization, demagnetized. Coercivity is usual ...

also known as the "staying magnetized" ability of a given magnet. Coercivity is weaker in disc or ring shapes, slightly stronger in cylinder or bar shapes, and strongest in horseshoe shapes. To increase the coercivity of horseshoe magnets, steel keepers or

magnet keeper A magnet keeper, also known historically as an armature, is a bar made from magnetically soft iron or steel, which is placed across the poles of a permanent magnet to help preserve the strength of the magnet by completing the magnetic circuit; ...

s are used. A magnetic field holds its strength best when the entire magnetic field is given the ability to loop through a

ferromagnetic Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagne ...

substance instead of air. The nearness of the horseshoe magnet’s poles facilitates the ability to use these magnet keepers more easily than other types of magnets. File:MagnetEZ.jpg, A horseshoe magnet made of AlNiCo, an iron alloy. The attached iron bar is a magnet keeper used to prevent demagnetization. File:Magnetic field of horseshoe magnet.png, Magnetic field of a horseshoe magnet. The field is greatest where the lines are densest, around the poles (lower) File:Magnetron magnet.JPG, Alnico horseshoe magnet used in a

magnetron The cavity magnetron is a high-power vacuum tube used in early radar systems and subsequently in microwave oven, microwave ovens and in linear particle accelerators. A cavity magnetron generates microwaves using the interaction of a stream of ...

tube in an early microwave oven. About 3 in (8 cm) long. File:Alnico horseshoe magnet assortment 1956.jpg, Assortment of AlNiCo horseshoe magnet shapes available from a manufacturer in 1956. File:Rectangular_Horseshoe_Magnet.jpg, A rectangular horseshoe magnet.

References

{{Magnetic states Types of magnets