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In the world around us, we can observe a force called gravity that pulls things towards Earth. On a smaller scale, we can see electrons that form the atoms that make up our planet. Yet, what we can't see are the forces that make these things possible, both on a micro and macro scale.Metals make relatively good conductors of heat, primarily because the delocalized electrons are free to transport thermal energy between atoms. However, unlike electrical conductivity, the thermal conductivity of a metal is nearly independent of temperature. T
ed mathematically by the Wiedemann–Franz law,
At a given temperature, each material has an electrical conductivity that determines the value of electric current when an electric potential is applied. Examples of good conductors include metals such as copper and gold, whereas glass and Teflon are poor conductors. In any dielectric material, the electrons remain bound to their respective atoms and the material behaves as an insulator. Most semiconductors have a variable level of conductivity that lies between the extremes of conduction and insulation.
The second measurement was of the charge of the electron. This was determined with a precision of better than 1% by Robert A. Millikan in his famous oil drop experiment in 1909. Together with the mass-to-charge ratio, the electron mass was thereby determined with reasonable precision. The value of mass that was found for the electron was initially met with surprise by physicists, since it was so small (less than 0.1%) compared to the known mass of a hydrogen atom. (Source:en.wikipedia.org)
The combination of the energy variation needed to create these particles, and the time during which they exist, fall under the threshold of detectability expressed by the Heisenberg uncertainty relation, ΔE · Δt ≥ Ä§. In effect, the energy needed to create these virtual particles, ΔE, can be "borrowed" from the vacuum for a period of time, Δt, so that their product is no more than the reduced Planck constant, Ä§ ≈
Electrons are the quantum glue of our world. Without electrons there would be no chemistry, and light would be unable to interact with matter. If electrons were only a little heavier or lighter than they are, the world would look radically different. But how can a particle which is so tiny that it has so far been considered point-like actually be weighed? This feat has now been achieved in a collaborative project involving physicists from the Max Planck Institute for Nuclear Physics in Heidelberg who "weighed" the mass of the electron 13 times more precisely than previously known. As electron mass is involved in fundamental physical constants, it is of significance to fundamental physics. (Source: www.mpg.de)