When water flows through the pipe, it is always affected by frictional resistance. When the free charge moves in a direction in the conductor to form a current, it is also hindered. Inside the metal conductor, there are both atoms and positively charged positive ions, as well as free electrons. Under the action of external power, when free electrons make directional motion inside the conductor, they collide with regularly arranged atoms and positive ions, and as a result, the directional motion of the electrons is hindered. The conductor, which blocks the passage of current, is called the resistance of the conductor.
Experiments have shown that the resistance of a conductor changes with temperature. As the temperature increases, the resistance of the metal will increase. The filament (tungsten wire) in the bulb, the temperature is only a few tens of degrees when not emitting light, the resistance is very small, reaching 2 000 ° C when the light is emitted, the resistance value of the filament is increased many times. When the bulb is used for a long time, the tungsten wire is easily broken, but the tungsten filament is broken most of the time when the lamp is turned on. This is because the filament temperature has not risen just after the lamp is turned on, and its resistance is relatively small. The current through the filament is much larger than when the light is illuminated. In 1911, the Dutch physicist Unnaus did an experiment: he cooled the mercury below minus 40 ° C and found that the resistance of mercury gradually decreased. When the temperature dropped to 4.173K (-268.977 ° C), he was surprised to find that the resistance of mercury suddenly disappeared.
Under extremely low temperature conditions, the resistance of mercury was “unmovedâ€. This discovery caused a sensation in the scientific community and attracted great attention. Later, it was discovered that some metals and alloys suddenly disappeared when the temperature dropped to a certain value. The phenomenon that this resistance suddenly disappears is called "superconductivity phenomenon", and the substance with superconductivity is called superconductor.
The discovery of superconductivity has opened up new areas for the exploration of energy conservation. Scientists are working hard to find superconducting materials with high critical temperatures to serve actual production.
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