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Image attribution: Created by Rama. Creative Commons Attribution-Share Alike 2.0 France via Wikimedia Commons |
All
electrical conductors have resistance. This can be useful (E.g.
electric elements which get hot for boiling water or room heating) or a
disadvantage (resulting in waste of power in transmission cables).
Because of electrical resistance, we have to use thicker cables to carry
larger currents. Superconductors are materials that have zero
resistance and huge currents can be carried by thin cables. Currently,
superconductive properties only exist at very low temperatures and
liquid helium or liquid nitrogen must be used to cool the materials. A
common use of superconductors is for the coils of the electromagnets of
MRI machines, allowing huge currents to be carried by reasonably sized
conductors. These magnets are necessary for generating the strong
magnetic fields required for imaging. They're also a component of the
electromagnets that generate the magnetic fields in particle
accelerators. The image shows a section of a superconducting cable
capable of carrying 12,500 amps and used for the Large Hadron Collider
at CERN. The top image is of an older conventional cable that could
carry the same current, requiring 25 heavy gauge individual cores.
An
electromagnet in its simplest form is a coil of wire, wrapped around a
former. You can make one by wrapping a couple of hundred of turns of
wire around a nail and connecting it to an AA cell. The magnet's
strength depends on the number of turns and also the magnitude of the
current. All electric motors use electromagnets to create the forces
required for motion of the shaft.