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Diffstat (limited to 'supcon.tex')
| -rw-r--r-- | supcon.tex | 24 |
1 files changed, 12 insertions, 12 deletions
@@ -15,11 +15,11 @@ Superconductors. The behavior of these types of materials is explained by quantum mechanics. Basically, when atoms form a solid, the atomic levels of the electrons combine to form bands. That is, over a finite range of energies there are states available to electrons. Since only one electron can occupy a given -state, the {\bf Pauli Exclusion Principle}, electrons will fill these states up -to some maximum, the Fermi Energy: $E_f$. A solid is a metal if it has an -energy band which is not full; the electrons are then free to move about, -making a metal a good conductor of electricity. If the solid has a band which -is completely full, with an energy gap to the next band, that solid will not +state, as described by the {\bf Pauli Exclusion Principle}, electrons will fill these states up +to some maximum: the Fermi Energy: $E_f$. A solid is a metal if it has an +energy band that is not full. The electrons are then free to move about, +making a metal a good conductor of electricity. If the solid has a band +that is completely full, with an energy gap to the next band, that solid will not conduct electricity very well, making it an insulator. A semiconductor is between a metal and insulator: while it has a full band (the valence band), the next band (the conduction band) is close enough in energy, and so the @@ -42,17 +42,17 @@ dissipation. superconductors will work in liquid nitrogen (at 77 K), which is relatively cheap and abundant. - Some fascinating facts about superconductors: they will carry + A fascinating fact about superconductors: they will carry a current nearly indefinitely, without resistance. Superconductors have a critical temperature, above which they lose their superconducting properties. Another striking demonstration of superconductivity is the \textbf{Meissner effect}. - Magnetic fields cannot penetrate superconducting surfaces, instead a + Magnetic fields cannot penetrate superconducting surfaces; instead a superconductor attempts to expel all magnetic field - lines. It is fairly simple to intuitively understand the Meissner effect, if you imagine a perfect - conductor of electricity. If placed in a magnetic field, - Faraday's Law says an induced current which opposes the field + lines. It is fairly simple to intuitively understand the Meissner effect if you imagine a perfect + conductor of electricity. If a superconductor placed in a magnetic field, + Faraday's Law says an induced current that opposes the field would be set up. But unlike in an ordinary metal, this induced current does not dissipate in a perfect conductor. So, this induced current would always be present to produce a field @@ -69,8 +69,8 @@ skin or in your eyes! \item Do not touch anything that has been immersed in liquid nitrogen until the item warms up to the room temperature. Use the provided tweezers to remove and place items in the liquid nitrogen. -\item Do not touch the superconductor, it contains poisonous materials!. -\item Beware of the current leads, they are carrying a lethal current! +\item Do not touch the superconductor: it contains poisonous materials! +\item Beware of the current leads: they are carrying a lethal current! \end{itemize} |