The classical example of thermionic emission is the emission of electrons from a hot cathodeinto a vacuum (also known asthermal electron emissionor theEdison effect) in a vacuum tube. The hot cathode can be a metal filament, a coated metal filament, or a separate structure of metal or carbides or borides of transition metals. Vacuum emission from metals tends to become significant only for temperatures over 1000 K. The science dealing with this phenomenon has been known as thermionics, but this name seems to be gradually falling into disuse.[ according to whom?] The term thermionic emission is now also used to refer to any thermally-excited charge emission process, even when the charge is emitted from one solid-stateregion into another. This process is crucially important in the operation of a variety of electronic devices and can be used for electricity generation(such as thermionic convertersand electrodynamic tethers) or cooling. The magnitude of the charge flow increases dramatically with increasing temperature. History The Edison effect in a diode tube. A diode tube is connected in two configurations, one has a flow of electrons and the other does not. Note that the arrows represent electron current, not conventional current. Because the electronwas
Posted on: Thu, 28 Aug 2014 06:01:53 +0000
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