Changes

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]],

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>

:<math>

\int \vec{B} \dot \mathrm{d}\vec{l} = \mu I

\int \vec{B} \cdot \mathrm{d}\vec{l} = \mu I

</math>

</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>

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>

B = \mu nI

B = \mu nI

</math>

</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.  

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==

==Applications==