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Horseshoe magnet

From Wikipedia, the free encyclopedia

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.
Magnetic fields of a horseshoe magnet visualized using iron filings.

A horseshoe magnet is either a permanent magnet or an electromagnet made in the shape of a horseshoe (in other words, in a U-shape). The permanent kind has become the most widely recognized symbol for magnets.[1]: 2  It is usually depicted as red and marked with 'North' and 'South' poles.[1]: 3  Although rendered obsolete in the 1950s by squat, cylindrical magnets made of modern materials,[1]: 3,467  horseshoe magnets are still regularly shown in elementary school textbooks.[1]: 3  Historically, they were a solution to the problem of making a compact magnet that does not destroy itself in its own demagnetizing field.[1]: 2 [2]

History

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In 1819, it was discovered that passing electric current through a piece of metal deflected a compass needle. Following this discovery, many other experiments surrounding 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.[3]

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.[3][4] 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.[4] This would lay the groundwork for development of the electrical telegraph and the future of world-wide telecommunications for the next century and more.[4]

Shape

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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.[5] 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 to flow along a more direct path between the poles and concentrates the magnetic field.[6]

The shape of the horseshoe magnet also drastically reduces its demagnetization over time.[7] This is due to coercivity also known as the "staying magnetized" ability of a given magnet.[7] Coercivity is weaker in disc or ring shapes, slightly stronger in cylinder or bar shapes, and strongest in horseshoe shapes.[6][7] To increase the coercivity of horseshoe magnets, steel keepers or magnet keepers are used.[7] A magnetic field holds its strength best when the entire magnetic field is given the ability to loop through a ferromagnetic substance instead of air.[8] The nearness of the horseshoe magnet’s poles facilitates the ability to use these magnet keepers more easily than other types of magnets.[8]

References

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  1. ^ a b c d e Coey, J. M. D. (2010). Magnetism and Magnetic Materials. Cambridge University Press. ISBN 978-0-511-67743-4.
  2. ^ "Why are Magnets Shaped like Horseshoes?". K&J Magnetics, Inc. Archived from the original on 24 December 2022. Retrieved 23 February 2023.
  3. ^ a b "Magnetism and Electromagnetism". Spark Museum. SPARK Museum of Electrical Invention. Retrieved 3 January 2021.
  4. ^ a b c Bellis, Mary (23 February 2019). "William Sturgeon and the Invention of the Electromagnet". ThoughtCo. Retrieved 3 January 2021.
  5. ^ "The Various Shapes of Magnets and Their Uses". Apex Magnets. Retrieved 3 January 2021.
  6. ^ a b "Temperature and Neodymium Magnets". K&J Magnetics. K&J Magnetics, Inc. Retrieved 3 January 2021.
  7. ^ a b c d "Why are Magnets Shaped like Horseshoes?". K&J Magnetics. K&J Magnetics, Inc. Retrieved 3 January 2021.
  8. ^ a b "Demagnetizing a Steel Nail". Sciencing. Retrieved 3 January 2021.