2006-10-10 10:10:04 · 8 answers · asked by toby w 1 in Science & Mathematics ➔ Physics
In 1911, Dutch physicist Heike Kamerlingh Onnes was astonished to find that the electrical resistance of mercury vanished below 4.2 Kelvin. Electrical resistance in metals is caused by the scattering of the conduction electrons by the impurity atoms. Obviously electrons repel each other. Let's say an electron passes near a positive ion. The attraction between them might slightly modify the vibration of the ion. This in turn could interact with a second electron nearby which will also be attracted to the ion. The net effect of these two interactions will be an apparent attractive force between the two electrons. The attraction is obviously very weak. In 1956, Cooper showed that if there was an attractive interaction, however weak, the lowest energy state of the system at T = 0 K would be one in which the electrons were paired. The pairs are therefore called Cooper pairs. If you have a pair of electrons, they can only be scattered if the energy involved is sufficient to break it up into single electrons. If less energy than that is available, they can not be scattered, and you have zero resistivity. The general theory of superconductivity was proposed by Bardeen, Cooper, and Schrieffer in 1957, and is called the BCS Theory.
2006-10-10 10:20:59 · answer #1 · answered by Anonymous · 1⤊ 1⤋
In copper some of the electrons are free and form an "electron gas". It is these free electrons that carry electricity. The speed they move - the drift velocity, depends on who often they get scattered by imperfections in the copper. The distance between individual scatterings is the mean free path. The shorter the free mean path the greater resistance. Adding impurities adds more scattering targets and hence shortens the mean free path and therefore increases resistance.
Hope this helps
2006-10-10 10:27:45 · answer #2 · answered by Mark G 7 · 1⤊ 0⤋
all the answers have been great, basically blocking electron flow.
just to clear something up for island girl, pure water is actually a very poor conductor of electricity, the impurities in water are actually what makes it conduct electricity! Things like dissolved salts (salt molecules break into electrically charged pieces) allow for electricity to flow. Free charge is needed for electricity to flow, in the case of copper this comes from the electron cloud around the copper atoms
2006-10-11 01:57:01 · answer #3 · answered by aussie_aussie9 1 · 0⤊ 0⤋
The impurities decreases the number of free electrons in the material, thus increasing its resistance.
2006-10-10 22:52:55 · answer #4 · answered by Sam 4 · 0⤊ 0⤋
Impurities increase resistance to the flow of electrons.
2006-10-10 10:12:41 · answer #5 · answered by luckyaz128 6 · 0⤊ 1⤋
As any Physics text book will tell you, good metallic conductors have loosely bound electrons in their outermost orbits (highest energy levels). Replacing some of these atoms with those of a metal without this property means fewer conductance electrons.
2006-10-10 10:17:43 · answer #6 · answered by DriverRob 4 · 2⤊ 0⤋
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2016-12-08 12:24:02 · answer #7 · answered by motato 4 · 0⤊ 0⤋
Think about water. If you add dirt to water it turns into mud and slows down anything that is trying to go through it. Water is conductive as well so if you have to many impurities it loses capacitance, right?
2006-10-10 10:20:19 · answer #8 · answered by island girl 2 · 0⤊ 1⤋