Dear Sir or Madam, website uses cookies, which are intended to record visits. This website does not use cookies that contain your personal information.

Do you allow the usage of cookies on this webpage?
Born on this day
Robbie Williams
Born Robbie Williams, English singer
7th week in year
13 February 2018

Important eventsBack

Thomas Edison observes the Edison effect.13.2.1880

Wikipedia (25 Feb 2013)

Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the binding potential, also known as work function of the metal. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions". After emission, a charge will initially be left behind in the emitting region that is equal in magnitude and opposite in sign to the total charge emitted. But if the emitter is connected to a battery, then this charge left behind will be neutralized by charge supplied by the battery, as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The thermionic emission of electrons is also known as thermal electron emission.

The classical example of thermionic emission is the emission of electrons from a hot cathode, into a vacuum (also known as the Edison 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.

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-state region into another. This process is crucially important in the operation of a variety of electronic devices and can be used for electricity generation (e.g., thermionic converter, electrodynamic tether) or cooling. The magnitude of the charge flow increases dramatically with increasing temperature.

" Beautiful moments of our lives."