Thermionic Work Function
The work function is also important in the theory of thermionic emission. Here the electron gains its energy from heat rather than photons. According to the Richardson-Dushman equation the emitted electron current density, J (A/m2), is related to the absolute temperature T by the equation:
where W is the work function of the metal, k is the Boltzmann constant and the proportionality constant A, known as Richardson's constant, is given by
where m and -e are the mass and charge of an electron, and h is the Planck constant.
Thermionic emission—electrons escaping from the heated negatively-charged filament (hot cathode)—is important in the operation of vacuum tubes. Tungsten, the common choice for vacuum tube filaments, has a work function of approximately 4.5 eV. Various oxide coatings can substantially reduce this.
Read more about this topic: Work Function
Famous quotes containing the words work and/or function:
“Art, whose honesty must work through artifice, cannot avoid cheating truth.”
—Laura Riding (1901–1991)
“Literature does not exist in a vacuum. Writers as such have a definite social function exactly proportional to their ability as writers. This is their main use.”
—Ezra Pound (1885–1972)