A horseshoe magnet is a magnet made in the shape of a horseshoe or a U-shape and has become the most widely recognized symbol for magnets. It was invented by

William Sturgeon 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. Early life Sturgeon was born on 22 May 1783 in Whittington, ...

in 1825. This type of magnet can be 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 wound into a coil. A current through the wire creates a magnetic field which is concentrated in the ...

. The main advantage of a horseshoe magnet over other types of magnets is that the magnetic poles are close together creating a much stronger magnetic field.

History

In 1819, it was discovered that passing

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...

through a piece of

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

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 ...

needle. Following this discovery, many other experiments surrounding

magnetism Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

were attempted. These experiments culminated in William Sturgeon wrapping wire around a

horseshoe-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a bell-shaped curve has the shape of the vertical ...

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 with symbol Fe (from la, ferrum) 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, right in f ...

. 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 telegraphs were point-to-point text messaging systems, primarily used from the 1840s until the late 20th century. It was the first electrical telecommunications system and the most widely used of a number of early messaging systems ...

and the future of world-wide

telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

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 magnet stronger. 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 to physics. For transport ph ...

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 demagnetized. Coercivity is usually measured in ...

also known as the "staying magnetized" ability of a given magnet. Coercivity is weaker in disc or ring shapes, slightly stronger in

cylinder A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infin ...

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) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...

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 Alnico is a family of iron alloys which in addition to iron are composed primarily of aluminium (Al), nickel (Ni), and cobalt (Co), hence the acronym ''al-ni-co''. They also include copper, and sometimes titanium. Alnico alloys are ferromagnetic, ...

, 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 currently in microwave ovens and linear particle accelerators. It generates microwaves using the interaction of a stream of electrons with a magnetic field while ...

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

External links

* {{Magnetic states Types of magnets