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An '''electromagnet''' is a device that generates a [[magnetic field]] when supplied with an [[electrical current]].<ref name=britannica>[https://www.britannica.com/science/electromagnet Electromagnet] from britannica.com</ref> It is often composed of a core of magnetic material (such as [[iron]]) surrounded by a coil of wire as a [[solenoid]]. The magnetic field created depends on the electrical current flowing through the coil, meaning that the strength of the magnetic field can be varied, the direction reveresed and unlike normal magnets, the magnetic field can be turned off. Electromagnets have a wide variety of uses, ranging from actuators and [[relays]] to [[MRI]] machines.<ref name=universetoday>[https://www.universetoday.com/39295/uses-of-electromagnets/ Uses of electromagnets] from universetoday.com</ref> The strongest electromagnet has a field strength of 45 Tesla.<ref>[https://nationalmaglab.org/about/around-the-lab/meet-the-magnets/meet-the-45-tesla-hybrid-magnet Meet the 45 Tesla Hybrid Magnet] from nationalmaglab.org</ref>
==History==
In 1820, the scientist Hans Christian Ørsted (1777-1851) observed that when he turned a circuit on, the needle of a nearby [[compass]] deviated from pointing North.<ref name=universetoday/> This is the first recorded discovery of how [[electricity]] and [[magnetism]] are related. In the very same year André-Marie Ampère noticed that a helical current carrying wire acted like a permanent magnet.<ref name=kenyon>[http://physics.kenyon.edu/EarlyApparatus/Electricity/Electromagnet/Electromagnet.html The Electromagnet] from physics.kenyon.edu</ref> Dominique François Jean Arago discovered that if an [[iron]] or [[steel]] bar was placed inside the helical coil, it would become magnetized. Later in 1824, William Sturgeon discovered that placing an iron core inside the coil significantly increased the magnetic field produced by the coil. Sturgeon improved the design further by bending the straight coil into a U shape, similar to the classic horseshoe magnet. Putting the poles closer to each other concentrated the field lines further and increasing the field. Finally Joseph Henry took a similar design to Sturgeon's but insulated the wires. Doing this, Henry created an electromagnet capable of lifting 3,600 pounds in 1832.<ref name=kenyon/>
==Physics==
Any [[electrical current]] in a wire produces a [[magnetic field]]. By taking a long wire and wrapping it up into a coil, one effectively concentrates the field or in other words increases it. The physics of electromagnets can be derived from [[Ampere's law]]. This states that, "for any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop."<ref name=amp>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/amplaw.html#c1 Ampere's Law] from hyperphysics.phy-astr.gsu.edu</ref> Mathematically, for a loop enclosing a current ''I'', this can be expressed as,
:<math>
\Sigma B_\parallel \Delta L = \mu I
</math>
where ''ΔL'' is a length element in the loop, ''μ'' is the permeability and <math display="inline">B_\parallel</math> is the component of the magnetic field parallel to ''ΔL''. In the limit of ''ΔL'' going to 0, this can be rewritten as an [[integral]],
:<math>
\int \vec{B} \dot \mathrm{d}\vec{l} = \mu I
</math>
Ampere's law can be used to derive the magnetic field of a straight wire. A straight wire has [[cylinder|cylindrical]] [[symmetry]], so it is expected the magnetic field will reflect this. It will therefore not have any component parallel to the wire. In fact the field will be circular, centred on the wire and parallel to the line element ''ΔL'' at any point. This means the field created is,<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c3 Magnetic Field of Current] from hyperphysics.phy-astr.gsu.edu</ref>
:<math>
B = \frac{\mu I}{2 \pi r}
</math>
where ''r'' is the radial distance of the point from the wire. In a [[solenoid]] with ''n'' coils per unit length, the field at its centre can be found as,<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html#c2 Solenoid Field from Ampere's Law] from hyperphysics.phy-astr.gsu.edu</ref>
:<math>
B = \mu nI
</math>
When cooled down to low temperatures, the coil may become [[superconductor|superconductor]] meaning it can carry a very large current. Since a larger current means a larger field, superconducting electromagnets are used when the large magnetic fields are required.
==Applications==
There are many applications for electromagnets. They are utilised for both [[science|scientific]] [[experiment]]s as well as in industrial applications since the strength of the [[magnetic field]] required can be easily met by adjusting the current accordingly. Examples of uses include:<ref name=universetoday/>
*[[Relay]]s
*Actuators
*[[Speaker]]s and electric bells
*Magnetic storage media like [[hard disk]]s and tape recorders
*[[Electric motor]]s
*[[Magnetic resonance imaging]] (MRI) machines and mass spectrometers
*Induction heating
*[[Particle accelerator]]
*Magnetic levitation such as Maglev trains
[[Solenoid]]s consist of a coil of wire enveloping a magnetic core, often composed of [[iron]].<ref name=universetoday/> Solenoids generate an almost uniform field in their centre making them useful in certain scientific experiments. They can also be used to control the movement of a component such as in fuel injectors. [[Superconductor|Superconducting]] magnets are able to generate fields on the order of 10-20 [[Tesla]], 150,000 times stronger than the Earth's magnetic field. They are often used in [[particle accelerator]]s such as the [[Large Hadron Collider]] at [[CERN]] which uses magnets that produce 8.3 Tesla using a current of 11,080 [[Amp]]s.<ref>[https://home.cern/about/engineering/pulling-together-superconducting-electromagnets Pulling together: Superconducting electromagnets] from home.cern</ref> Superconducting magnets are also used in [[Magnetic resonance imaging|MRI machine]]s, and typically produce a field between 0.5-2.0 Tesla.<ref>[https://science.howstuffworks.com/mri1.htm How MRI Works] from science.howstuffworks.com</ref> There are also more theoretical applications such as [[ion]] propulsion systems on spacecraft.<ref name=universetoday/>
==References==
{{reflist}}
==See also==
*[[Magnet]]
*[[Magnetic field]]
*[[Solenoid]]
[[Category:Physics]]
[[Category:Electromagnetism]]
[[Category:Engineering]]
==History==
In 1820, the scientist Hans Christian Ørsted (1777-1851) observed that when he turned a circuit on, the needle of a nearby [[compass]] deviated from pointing North.<ref name=universetoday/> This is the first recorded discovery of how [[electricity]] and [[magnetism]] are related. In the very same year André-Marie Ampère noticed that a helical current carrying wire acted like a permanent magnet.<ref name=kenyon>[http://physics.kenyon.edu/EarlyApparatus/Electricity/Electromagnet/Electromagnet.html The Electromagnet] from physics.kenyon.edu</ref> Dominique François Jean Arago discovered that if an [[iron]] or [[steel]] bar was placed inside the helical coil, it would become magnetized. Later in 1824, William Sturgeon discovered that placing an iron core inside the coil significantly increased the magnetic field produced by the coil. Sturgeon improved the design further by bending the straight coil into a U shape, similar to the classic horseshoe magnet. Putting the poles closer to each other concentrated the field lines further and increasing the field. Finally Joseph Henry took a similar design to Sturgeon's but insulated the wires. Doing this, Henry created an electromagnet capable of lifting 3,600 pounds in 1832.<ref name=kenyon/>
==Physics==
Any [[electrical current]] in a wire produces a [[magnetic field]]. By taking a long wire and wrapping it up into a coil, one effectively concentrates the field or in other words increases it. The physics of electromagnets can be derived from [[Ampere's law]]. This states that, "for any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop."<ref name=amp>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/amplaw.html#c1 Ampere's Law] from hyperphysics.phy-astr.gsu.edu</ref> Mathematically, for a loop enclosing a current ''I'', this can be expressed as,
:<math>
\Sigma B_\parallel \Delta L = \mu I
</math>
where ''ΔL'' is a length element in the loop, ''μ'' is the permeability and <math display="inline">B_\parallel</math> is the component of the magnetic field parallel to ''ΔL''. In the limit of ''ΔL'' going to 0, this can be rewritten as an [[integral]],
:<math>
\int \vec{B} \dot \mathrm{d}\vec{l} = \mu I
</math>
Ampere's law can be used to derive the magnetic field of a straight wire. A straight wire has [[cylinder|cylindrical]] [[symmetry]], so it is expected the magnetic field will reflect this. It will therefore not have any component parallel to the wire. In fact the field will be circular, centred on the wire and parallel to the line element ''ΔL'' at any point. This means the field created is,<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c3 Magnetic Field of Current] from hyperphysics.phy-astr.gsu.edu</ref>
:<math>
B = \frac{\mu I}{2 \pi r}
</math>
where ''r'' is the radial distance of the point from the wire. In a [[solenoid]] with ''n'' coils per unit length, the field at its centre can be found as,<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html#c2 Solenoid Field from Ampere's Law] from hyperphysics.phy-astr.gsu.edu</ref>
:<math>
B = \mu nI
</math>
When cooled down to low temperatures, the coil may become [[superconductor|superconductor]] meaning it can carry a very large current. Since a larger current means a larger field, superconducting electromagnets are used when the large magnetic fields are required.
==Applications==
There are many applications for electromagnets. They are utilised for both [[science|scientific]] [[experiment]]s as well as in industrial applications since the strength of the [[magnetic field]] required can be easily met by adjusting the current accordingly. Examples of uses include:<ref name=universetoday/>
*[[Relay]]s
*Actuators
*[[Speaker]]s and electric bells
*Magnetic storage media like [[hard disk]]s and tape recorders
*[[Electric motor]]s
*[[Magnetic resonance imaging]] (MRI) machines and mass spectrometers
*Induction heating
*[[Particle accelerator]]
*Magnetic levitation such as Maglev trains
[[Solenoid]]s consist of a coil of wire enveloping a magnetic core, often composed of [[iron]].<ref name=universetoday/> Solenoids generate an almost uniform field in their centre making them useful in certain scientific experiments. They can also be used to control the movement of a component such as in fuel injectors. [[Superconductor|Superconducting]] magnets are able to generate fields on the order of 10-20 [[Tesla]], 150,000 times stronger than the Earth's magnetic field. They are often used in [[particle accelerator]]s such as the [[Large Hadron Collider]] at [[CERN]] which uses magnets that produce 8.3 Tesla using a current of 11,080 [[Amp]]s.<ref>[https://home.cern/about/engineering/pulling-together-superconducting-electromagnets Pulling together: Superconducting electromagnets] from home.cern</ref> Superconducting magnets are also used in [[Magnetic resonance imaging|MRI machine]]s, and typically produce a field between 0.5-2.0 Tesla.<ref>[https://science.howstuffworks.com/mri1.htm How MRI Works] from science.howstuffworks.com</ref> There are also more theoretical applications such as [[ion]] propulsion systems on spacecraft.<ref name=universetoday/>
==References==
{{reflist}}
==See also==
*[[Magnet]]
*[[Magnetic field]]
*[[Solenoid]]
[[Category:Physics]]
[[Category:Electromagnetism]]
[[Category:Engineering]]