US DEPARTMENT OF ENERGY / SCIENCE PHOTO LIBRARY US DEPARTMENT OF ENERGY / SCIENCE PHOTO LIBRARY
A pellet of a superconducting compound demonstrating the Meissner effect. Superconductors are materials that have no electrical resistance, usually when cooled to extremely low temperatures. The pellet seen here is a ceramic compound of copper oxide with barium and lanthanum. When cooled to about 20 Kelvin (-253 Celsius) with liquid hydrogen, the pellet becomes superconducting. The Meissner effect is the exclusion of magnetic fields by a superconductor. Normally the pellet would rest within the field between the poles of the magnet seen here, but when superconducting it is expelled by the field.
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