MadSci Network: Physics |
For "ordinary" Ohmic resistance, there needs to be a medium for the electrons to flow through. In that environment, a vacuum is like an insulator and no current (i.e., electron flow) exists. However, not all currents and resistances are Ohmic -- an example is the semiconductor. Therefore, it is possible to have a current across a vacuum. One way to accomplish this is to break the vacuum, temporarily, by applying enough potential difference (voltage) to the "sides" of the vacuum. In practice a perfect vacuum cannot be created because all the materials that would surround such a space have a finite pressure, which means that they expel some atoms or molecules into the space. Applying a (large) voltage to the surrounding material increases the pressure and causes electrons to flow. A second method to accomplish "electron flow" through a vacuum would be via the photoelectric effect. Photons can travel from one side of the vacuum, through the empty space (recall, that photons do not need a medium through which to propagate) and liberate electrons on the other side. These liberated electrons are called photoelectrons. Since the effect is that electrons are moving from one side of the vacumm to the other side, there is a current through the vacuum. Perhaps, it is more correct to say that energy flowed through the vacuum. I see no reason why just a decrease in atmospheric pressure would have an effect on resistance, but a decrease in pressure and matter will effect Ohmic resistance.
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