View source for Physics:Horseshoe magnet

{{short description|Magnet in the shape of a horseshoe}}
{{Electromagnetism|cTopic = [[Physics:Magnetostatics|Magnetostatics]]}}
[[File:VFPt horseshoe-magnet.svg|thumb|upright=0.9|Horseshoe magnet with computed magnetic field lines. The two magnetic poles are in close vicinity, which concentrates the field lines and creates a strong magnetic field.]]
[[File:Horseshoe_Magnetic_Filings_(Flipped_180).jpg|thumb|upright=.9|Magnetic fields of a horseshoe magnet visualized using iron filings.]]

A '''horseshoe magnet''' is either a [[Physics:Magnet|permanent]] magnet or an [[Physics:Electromagnet|electromagnet]] made in the shape of a [[Engineering:Horseshoe|horseshoe]] (in other words, in a U-shape). The permanent kind has become the most widely recognized symbol for magnets.<ref name="Coey Magnetism">{{cite book |last1=Coey |first1=J. M. D. |title=Magnetism and Magnetic Materials|date=2010 |publisher={{wipe|Cambridge University Press}} |isbn=978-0-511-67743-4 |url=https://books.google.com/books?id=bqcgAwAAQBAJ&dq=%22making%20a%20reasonably%20compact%20magnet%20which%20will%20not%20destroy%20itself%20in%20its%20own%22&pg=PA2 |language=en}}</ref>{{rp|page=2}} It is usually depicted as red and marked with 'North' and 'South' poles.<ref name="Coey Magnetism"/>{{rp|page=3}} Although rendered obsolete in the 1950s by squat, cylindrical magnets made of modern materials,<ref name="Coey Magnetism"/>{{rp|page=3,467}} horseshoe magnets are still regularly shown in elementary school textbooks.<ref name="Coey Magnetism"/>{{rp|page=3}} Historically, they were a solution to the problem of making a compact magnet that does not destroy itself in its own demagnetizing field.<ref name="Coey Magnetism"/>{{rp|page=2}}<ref name="kjmagnetics">{{cite web |title= Why are Magnets Shaped like Horseshoes? |url=https://www.kjmagnetics.com/blog.asp?p=why-horseshoes |website=K&J Magnetics, Inc. |language=en |access-date=23 February 2023 |archive-url=https://web.archive.org/web/20221224192957/https://www.kjmagnetics.com/blog.asp?p=why-horseshoes |archive-date=24 December 2022 |url-status=live}}</ref>

== History ==
In 1819, it was discovered that passing [[Physics:Electric current|electric current]] through a piece of [[Chemistry:Metal|metal]] deflected a [[Physics:Compass|compass]] needle. Following this discovery, many other experiments surrounding [[Physics:Magnetism|magnetism]] were attempted. These experiments culminated in William Sturgeon wrapping wire around a horseshoe-shaped piece of iron and running electric current through the wires creating the first horseshoe magnet.<ref name="Spark Museum">{{cite web |url=http://www.sparkmuseum.com/MAGNET.HTM#:~:text=In%201825%20William%20Sturgeon%20developed,horseshoe%2Dshaped%20piece%20of%20iron.&text=The%20seven%2Dounce%20magnet%20was,current%20from%20a%20single%20cell |title=Magnetism and Electromagnetism |publisher = SPARK Museum of Electrical Invention | website=Spark Museum |access-date=3 January 2021}}</ref>

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 [[Chemistry:Iron|iron]].<ref name="Spark Museum"/><ref name="ThoughtCo">{{cite web |url=https://www.thoughtco.com/who-invented-the-electromagnet-1991678 |title=William Sturgeon and the Invention of the Electromagnet |last=Bellis |first=Mary |date=23 February 2019 |website=ThoughtCo |access-date=3 January 2021}}</ref> 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.<ref name="ThoughtCo"/> This would lay the groundwork for development of the electrical telegraph and the future of world-wide telecommunications for the next century and more.<ref name="ThoughtCo"/>

== Shape ==

The shape of the magnet was originally created as a replacement for the bar magnet as it makes the magnet stronger.<ref name="Apex">{{cite web |url=https://www.apexmagnets.com/news-how-tos/the-various-shapes-of-magnets-and-their-uses/ |title=The Various Shapes of Magnets and Their Uses |website=Apex Magnets |access-date=3 January 2021}}</ref> 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 [[Physics:Flux|flux]] to flow along a more direct path between the poles and concentrates the magnetic field.<ref name="K&J-1">{{cite web |url=https://www.kjmagnetics.com/blog.asp?p=temperature-and-neodymium-magnets |title=Temperature and Neodymium Magnets |publisher = K&J Magnetics, Inc. | website=K&J Magnetics |access-date=3 January 2021}}</ref>

The shape of the horseshoe magnet also drastically reduces its demagnetization over time.<ref name="K&J-2">{{cite web |url=https://www.kjmagnetics.com/blog.asp?p=why-horseshoes |title=Why are Magnets Shaped like Horseshoes? |publisher = K&J Magnetics, Inc. | website=K&J Magnetics |access-date=3 January 2021}}</ref> This is due to [[Physics:Coercivity|coercivity]] also known as the "staying magnetized" ability of a given magnet.<ref name="K&J-2"/> Coercivity is weaker in disc or ring shapes, slightly stronger in [[Cylinder|cylinder]] or bar shapes, and strongest in horseshoe shapes.<ref name="K&J-1"/><ref name="K&J-2"/> To increase the coercivity of horseshoe magnets, steel keepers or [[Physics:Magnet keeper|magnet keeper]]s are used.<ref name="K&J-2"/> A magnetic field holds its strength best when the entire magnetic field is given the ability to loop through a [[Physics:Ferromagnetic|ferromagnetic]] substance instead of air.<ref name="Sciencing">{{cite web |url=https://sciencing.com/demagnetizing-steel-nail-17841.html |title=Demagnetizing a Steel Nail | website=Sciencing |access-date=3 January 2021}}</ref> The nearness of the horseshoe magnet’s poles facilitates the ability to use these magnet keepers more easily than other types of magnets.<ref name="Sciencing"/>

<gallery mode="packed" heights="180">
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 tube in an early microwave oven. About 3&nbsp;in (8&nbsp;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.
</gallery>

== References ==
{{Reflist}}

== External links ==

{{Magnetic states}}

[[Category:Types of magnets]]

{{Sourceattribution|Horseshoe magnet}}