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:
“It is the work of a brave man surely, in whom there was no guile! He rounded this water with his hand, deepened and clarified it in his thought, and in his will bequeathed it to Concord. I see by its face that it is visited by the same reflection; and I can almost say, Walden, is it you?”
—Henry David Thoreau (18171862)
“My function in life is not to be a politician in Parliament: it is to get something done.”
—Bernadette Devlin (b. 1947)