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Question

Which metal is used as an electron emitter?


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Solution

  1. The metal or metallic substances used to construct a thermionic emitter should have some main features.
  2. It should have a low work function.
  3. A low work function helps to emit electrons from the cathode surface in a comparatively lower temperature.
  4. It should have a high melting point.
  5. Tungsten metal is used as an electron emitter as it has a very high melting point (3655K) and moderate work function.
  6. It has a work function of about 4.52eV. It starts emission at 2500K.
  7. If thoriated tungsten (which is coated with carbon and thorium) is used work function reduces to 2.6eV and emission begins at 2000K.
  8. If tungsten is coated with metals like barium and strontium oxide work, function reduces to 1eV and emission begins at 1000K and a good quality of electrons is obtained.

Thus, Tungsten is used as an electron emitter.


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