The resistance of metals varies with their temperature. when they get hot, their resistance increases. When they cool, their resistance falls. The resistance of some metals and alloys steadily decreases as their temperature is lowered, then falls suddenly to a negligible value at temperatures a few degrees above absolute zero (-273˚C). In other words, these materials have almost no resistance to an electric current at very low temperatures. They become almost perfect conductors. This is called super conductivity. It occurs only with certain materials, for example lead, and only at very low temperatures.
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