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It was initially reported in 1873 by Guthrie in Britain. While doing work on charged objects, Professor Guthrie discovered that a red-hot iron sphere with a negative charge would lose its charge (discharging the extra electrons into the vacuum). He also found that this did not happen if the sphere had a positive charge.
Owen Richardson worked with thermionic emission and received a Nobel prize in 1928 "for his work on the thermionic phenomenonand especially for the discovery of the law named after him".
In any metal, there are one or two electrons per atom that are free to move from atom to atom. This is sometimes referred to as a "sea of electrons". Their velocities follow a statistical distribution, rather than being uniform, and occasionally an electron will have enough velocity to exit the metal without being pulled back in. The minimum amount of energy needed for an electron to leave the surface is called the work function, and varies from metal to metal. A thin oxide coating is often applied to metal surfaces in vacuum tubes to give a lower work function, as it is easier for electrons to leave the surface of the oxide.
The Richardson-Dushmann equation states that the emitted current density J (A/m2) is related to temperature T by the equation:
where T is the metal temperature in Kelvins, W is the work function of the metal, k is the Boltzmann constant, and A is Richardson's constant.
The exponent in the equation shows that the amount of current emitted increases drastically with temperature.
The thermionic emission equations are important in semiconductor design.
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.
The effect was accidentally rediscovered in 1880, by Thomas EdisonThomas Alva Edison ( February 11, 1847 October 18, 1931) was an inventor and businessman who developed many important devices. The Wizard of Menlo Park was one of the first inventors to apply the principles of mass production to the process of invention., while trying to discover the reason for breakage of lamp filaments and uneven blackening (darkest near one terminal of the filament) of the bulbs in his incandescent lamps.
Edison built a bulb with the inside surface covered with tin foilTin foil or tinfoil is a thin leaf made of tin. Commonly, it is a misnomer for aluminium foil, as tin foil was commercially available before the aluminium counterpart, and some people continue to refer to the new product by the name of the old one. Tin fo. When he connected the foil to the lamp filament through a galvanometerA Galvanometer is an electromechanical transducer. It produces a rotary motion, through a limited arc, in response to electric current flowing through its coil. The name Galvanometer has been applied to devices used in measuring, recording, and positionin, with the foil dropped to a negative voltage with respect to the filament, nothing happened (because the cold foil electrode was not emitting electrons). But, when he raised the foil to a positive voltage with respect to the filament, a small current flow was indicated on the galvanometer, as electrons being emitted from the hot filament were attracted to the plate, and completed the circuit. This one-way flow of current was called the Edison effect (although the term is occasionally used to refer to thermionic emission itself).
Edison saw no use for this effect, and although he patented it in 1883Events January January 16 The Pendleton Civil Service Reform Act, establishing the United States Civil service, is passed January 19 The first electric lighting system employing overhead wires begins service ( Roselle, New Jersey) It was built by Thomas E, he did not study it any further.