Magnet | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-06-26

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Magnet


00:02:30 1 Discovery and development
00:03:35 2 Physics
00:03:44 2.1 Magnetic field
00:04:26 2.2 Magnetic moment
00:05:58 2.3 Magnetization
00:06:58 2.4 Modelling magnets
00:09:24 2.5 Polarity
00:10:20 2.6 Magnetic materials
00:13:18 3 Common uses
00:19:46 4 Medical issues and safety
00:21:30 5 Magnetizing ferromagnets
00:22:57 6 Demagnetizing ferromagnets
00:24:24 7 Types of permanent magnets
00:24:34 7.1 Magnetic metallic elements
00:25:39 7.2 Composites
00:28:02 7.3 Rare-earth magnets
00:28:40 7.4 Single-molecule magnets (SMMs) and single-chain magnets (SCMs)
00:30:00 7.5 Nano-structured magnets
00:30:21 7.6 Rare-earth-free permanent magnets
00:31:01 7.7 Costs
00:32:00 7.8 Temperature
00:32:54 8 Electromagnets
00:34:21 9 Units and calculations
00:36:23 9.1 Fields of a magnet
00:37:09 9.2 Calculating the magnetic force
00:37:30 9.2.1 Pull force of a single magnet
00:37:44 9.2.2 Force between two magnetic poles
00:38:16 9.2.3 Force between two nearby magnetized surfaces of area iA/i
00:39:13 9.2.4 Force between two bar magnets
00:39:20 9.2.5 Force between two cylindrical magnets
00:40:33 10 See also
00:40:43 11 Notes
00:42:15 12 References
00:43:43 13 External links
00:45:06 Force between two bar magnets
00:47:48 Force between two cylindrical magnets
00:52:45 See also



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SUMMARY
=======
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets. 
A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity.  The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.
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.  Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.